glsl2: Fix reversed value of step().

It's 0.0 if x < edge, not 1.0.  Partial fix for glsl-fs-step.
diff --git a/src/glsl/builtin_function.cpp b/src/glsl/builtin_function.cpp
index 626ba4e..811c5b2 100644
--- a/src/glsl/builtin_function.cpp
+++ b/src/glsl/builtin_function.cpp
@@ -2164,15 +2164,15 @@
    "     (parameters\n"
    "       (declare (in) float edge)\n"
    "       (declare (in) float x))\n"
-   "     ((return (expression float b2f (expression bool < (var_ref x) (var_ref edge))))))\n"
+   "     ((return (expression float b2f (expression bool >= (var_ref x) (var_ref edge))))))\n"
    "\n"
    "   (signature vec2\n"
    "     (parameters\n"
    "       (declare (in) float edge)\n"
    "       (declare (in) vec2 x))\n"
    "     ((declare () vec2 t)\n"
-   "      (assign (constant bool (1)) (swiz x (var_ref t)) (expression float b2f (expression bool < (swiz x (var_ref x))(var_ref edge))))\n"
-   "      (assign (constant bool (1)) (swiz y (var_ref t)) (expression float b2f (expression bool < (swiz y (var_ref x))(var_ref edge))))\n"
+   "      (assign (constant bool (1)) (swiz x (var_ref t)) (expression float b2f (expression bool >= (swiz x (var_ref x))(var_ref edge))))\n"
+   "      (assign (constant bool (1)) (swiz y (var_ref t)) (expression float b2f (expression bool >= (swiz y (var_ref x))(var_ref edge))))\n"
    "      (return (var_ref t))))\n"
    "\n"
    "   (signature vec3\n"
@@ -2180,9 +2180,9 @@
    "       (declare (in) float edge)\n"
    "       (declare (in) vec3 x))\n"
    "     ((declare () vec3 t)\n"
-   "      (assign (constant bool (1)) (swiz x (var_ref t)) (expression float b2f (expression bool < (swiz x (var_ref x))(var_ref edge))))\n"
-   "      (assign (constant bool (1)) (swiz y (var_ref t)) (expression float b2f (expression bool < (swiz y (var_ref x))(var_ref edge))))\n"
-   "      (assign (constant bool (1)) (swiz z (var_ref t)) (expression float b2f (expression bool < (swiz z (var_ref x))(var_ref edge))))\n"
+   "      (assign (constant bool (1)) (swiz x (var_ref t)) (expression float b2f (expression bool >= (swiz x (var_ref x))(var_ref edge))))\n"
+   "      (assign (constant bool (1)) (swiz y (var_ref t)) (expression float b2f (expression bool >= (swiz y (var_ref x))(var_ref edge))))\n"
+   "      (assign (constant bool (1)) (swiz z (var_ref t)) (expression float b2f (expression bool >= (swiz z (var_ref x))(var_ref edge))))\n"
    "      (return (var_ref t))))\n"
    "\n"
    "   (signature vec4\n"
@@ -2190,10 +2190,10 @@
    "       (declare (in) float edge)\n"
    "       (declare (in) vec4 x))\n"
    "     ((declare () vec4 t)\n"
-   "      (assign (constant bool (1)) (swiz x (var_ref t)) (expression float b2f (expression bool < (swiz x (var_ref x))(var_ref edge))))\n"
-   "      (assign (constant bool (1)) (swiz y (var_ref t)) (expression float b2f (expression bool < (swiz y (var_ref x))(var_ref edge))))\n"
-   "      (assign (constant bool (1)) (swiz z (var_ref t)) (expression float b2f (expression bool < (swiz z (var_ref x))(var_ref edge))))\n"
-   "      (assign (constant bool (1)) (swiz w (var_ref t)) (expression float b2f (expression bool < (swiz w (var_ref x))(var_ref edge))))\n"
+   "      (assign (constant bool (1)) (swiz x (var_ref t)) (expression float b2f (expression bool >= (swiz x (var_ref x))(var_ref edge))))\n"
+   "      (assign (constant bool (1)) (swiz y (var_ref t)) (expression float b2f (expression bool >= (swiz y (var_ref x))(var_ref edge))))\n"
+   "      (assign (constant bool (1)) (swiz z (var_ref t)) (expression float b2f (expression bool >= (swiz z (var_ref x))(var_ref edge))))\n"
+   "      (assign (constant bool (1)) (swiz w (var_ref t)) (expression float b2f (expression bool >= (swiz w (var_ref x))(var_ref edge))))\n"
    "      (return (var_ref t))))\n"
    "\n"
    "   (signature vec2\n"
@@ -2201,8 +2201,8 @@
    "       (declare (in) vec2 edge)\n"
    "       (declare (in) vec2 x))\n"
    "     ((declare () vec2 t)\n"
-   "      (assign (constant bool (1)) (swiz x (var_ref t)) (expression float b2f (expression bool < (swiz x (var_ref x))(swiz x (var_ref edge)))))\n"
-   "      (assign (constant bool (1)) (swiz y (var_ref t)) (expression float b2f (expression bool < (swiz y (var_ref x))(swiz y (var_ref edge)))))\n"
+   "      (assign (constant bool (1)) (swiz x (var_ref t)) (expression float b2f (expression bool >= (swiz x (var_ref x))(swiz x (var_ref edge)))))\n"
+   "      (assign (constant bool (1)) (swiz y (var_ref t)) (expression float b2f (expression bool >= (swiz y (var_ref x))(swiz y (var_ref edge)))))\n"
    "      (return (var_ref t))))\n"
    "\n"
    "   (signature vec3\n"
@@ -2210,9 +2210,9 @@
    "       (declare (in) vec3 edge)\n"
    "       (declare (in) vec3 x))\n"
    "     ((declare () vec3 t)\n"
-   "      (assign (constant bool (1)) (swiz x (var_ref t)) (expression float b2f (expression bool < (swiz x (var_ref x))(swiz x (var_ref edge)))))\n"
-   "      (assign (constant bool (1)) (swiz y (var_ref t)) (expression float b2f (expression bool < (swiz y (var_ref x))(swiz y (var_ref edge)))))\n"
-   "      (assign (constant bool (1)) (swiz z (var_ref t)) (expression float b2f (expression bool < (swiz z (var_ref x))(swiz z (var_ref edge)))))\n"
+   "      (assign (constant bool (1)) (swiz x (var_ref t)) (expression float b2f (expression bool >= (swiz x (var_ref x))(swiz x (var_ref edge)))))\n"
+   "      (assign (constant bool (1)) (swiz y (var_ref t)) (expression float b2f (expression bool >= (swiz y (var_ref x))(swiz y (var_ref edge)))))\n"
+   "      (assign (constant bool (1)) (swiz z (var_ref t)) (expression float b2f (expression bool >= (swiz z (var_ref x))(swiz z (var_ref edge)))))\n"
    "      (return (var_ref t))))\n"
    "\n"
    "   (signature vec4\n"
@@ -2220,10 +2220,10 @@
    "       (declare (in) vec4 edge)\n"
    "       (declare (in) vec4 x))\n"
    "     ((declare () vec4 t)\n"
-   "      (assign (constant bool (1)) (swiz x (var_ref t)) (expression float b2f (expression bool < (swiz x (var_ref x))(swiz x (var_ref edge)))))\n"
-   "      (assign (constant bool (1)) (swiz y (var_ref t)) (expression float b2f (expression bool < (swiz y (var_ref x))(swiz y (var_ref edge)))))\n"
-   "      (assign (constant bool (1)) (swiz z (var_ref t)) (expression float b2f (expression bool < (swiz y (var_ref x))(swiz z (var_ref edge)))))\n"
-   "      (assign (constant bool (1)) (swiz w (var_ref t)) (expression float b2f (expression bool < (swiz w (var_ref x))(swiz w (var_ref edge)))))\n"
+   "      (assign (constant bool (1)) (swiz x (var_ref t)) (expression float b2f (expression bool >= (swiz x (var_ref x))(swiz x (var_ref edge)))))\n"
+   "      (assign (constant bool (1)) (swiz y (var_ref t)) (expression float b2f (expression bool >= (swiz y (var_ref x))(swiz y (var_ref edge)))))\n"
+   "      (assign (constant bool (1)) (swiz z (var_ref t)) (expression float b2f (expression bool >= (swiz y (var_ref x))(swiz z (var_ref edge)))))\n"
+   "      (assign (constant bool (1)) (swiz w (var_ref t)) (expression float b2f (expression bool >= (swiz w (var_ref x))(swiz w (var_ref edge)))))\n"
    "      (return (var_ref t))))\n"
    "))\n"
    "\n"