i965: Add INTEL_DEBUG=glsl_force to force brw_wm_glsl.c.

I keep finding the desire to force this path to debug it instead of
cooking up goofy-looking testcases to do so.

src/mesa/drivers/dri/i965/brw_wm_glsl.c

@@ -23,6 +23,9 @@ GLboolean brw_wm_is_glsl(const struct gl_fragment_program *fp)
 {
     int i;
 
+    if (INTEL_DEBUG & DEBUG_GLSL_FORCE)
+       return GL_TRUE;
+
     for (i = 0; i < fp->Base.NumInstructions; i++) {
 	const struct prog_instruction *inst = &fp->Base.Instructions[i];
 	switch (inst->Opcode) {

src/mesa/drivers/dri/intel/intel_context.c

@@ -444,6 +444,7 @@ static const struct dri_debug_control debug_control[] = {
    { "sing",  DEBUG_SINGLE_THREAD },
    { "thre",  DEBUG_SINGLE_THREAD },
    { "wm",    DEBUG_WM },
+   { "glsl_force", DEBUG_GLSL_FORCE },
    { "urb",   DEBUG_URB },
    { "vs",    DEBUG_VS },
    { NULL,    0 }

src/mesa/drivers/dri/intel/intel_context.h

@@ -342,6 +342,7 @@ extern int INTEL_DEBUG;
 #define DEBUG_WM        0x800000
 #define DEBUG_URB       0x1000000
 #define DEBUG_VS        0x2000000
+#define DEBUG_GLSL_FORCE 0x4000000
 
 #define DBG(...) do {						\
 	if (INTEL_DEBUG & FILE_DEBUG_FLAG)			\