Add EmitHighLevelInstructions, EmitComments booleans to gl_shader_state.

These control code generation options.  May be overridden by drivers, debuggers, etc.
diff --git a/src/mesa/shader/shader_api.c b/src/mesa/shader/shader_api.c
index 70ceb70..48ba8b6 100644
--- a/src/mesa/shader/shader_api.c
+++ b/src/mesa/shader/shader_api.c
@@ -196,16 +196,20 @@
 }
 
 
+/**
+ * Initialize context's shader state.
+ */
 void
 _mesa_init_shader_state(GLcontext * ctx)
 {
-   /* no-op */
+   /* Device drivers may override these to control what kind of instructions
+    * are generated by the GLSL compiler.
+    */
+   ctx->Shader.EmitHighLevelInstructions = GL_TRUE;
+   ctx->Shader.EmitComments = GL_FALSE;
 }
 
 
-
-
-
 /**
  * Copy string from <src> to <dst>, up to maxLength characters, returning
  * length of <dst> in <length>.
@@ -227,8 +231,6 @@
 }
 
 
-
-
 /**
  * Called via ctx->Driver.AttachShader()
  */