glx: turn LIBGL_ALWAYS_INDIRECT into a boolean

Instead of setting based on set/unset, allow users to use boolean values.
In the docs, use `ALWAYS=true` instead of `ALWAYS=1` as it's clearer IMO.

Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
diff --git a/docs/envvars.html b/docs/envvars.html
index b70528f..aeb5ff2 100644
--- a/docs/envvars.html
+++ b/docs/envvars.html
@@ -29,7 +29,7 @@
 <li>LIBGL_DEBUG - If defined debug information will be printed to stderr.
    If set to 'verbose' additional information will be printed.
 <li>LIBGL_DRIVERS_PATH - colon-separated list of paths to search for DRI drivers
-<li>LIBGL_ALWAYS_INDIRECT - forces an indirect rendering context/connection.
+<li>LIBGL_ALWAYS_INDIRECT - if set to `true`, forces an indirect rendering context/connection.
 <li>LIBGL_ALWAYS_SOFTWARE - if set to `true`, always use software rendering
 <li>LIBGL_NO_DRAWARRAYS - if set do not use DrawArrays GLX protocol (for debugging)
 <li>LIBGL_SHOW_FPS - print framerate to stdout based on the number of glXSwapBuffers
diff --git a/docs/libGL.txt b/docs/libGL.txt
index 839e330..b69b8c0 100644
--- a/docs/libGL.txt
+++ b/docs/libGL.txt
@@ -59,7 +59,7 @@
 Indirect Rendering
 
 You can force indirect rendering mode by setting the LIBGL_ALWAYS_INDIRECT
-environment variable.  Hardware acceleration will not be used.
+environment variable to `true`.  Hardware acceleration will not be used.
 
 
 
diff --git a/src/glx/glxext.c b/src/glx/glxext.c
index cd9a3ba..4021939 100644
--- a/src/glx/glxext.c
+++ b/src/glx/glxext.c
@@ -907,7 +907,7 @@
    dpyPriv->glXDrawHash = __glxHashCreate();
 
 #if defined(GLX_DIRECT_RENDERING) && !defined(GLX_USE_APPLEGL)
-   glx_direct = (getenv("LIBGL_ALWAYS_INDIRECT") == NULL);
+   glx_direct = !env_var_as_boolean("LIBGL_ALWAYS_INDIRECT", false);
    glx_accel = !env_var_as_boolean("LIBGL_ALWAYS_SOFTWARE", false);
 
    dpyPriv->drawHash = __glxHashCreate();