r300-gallium: Enable GLSL for r500.

Before you get all excited, this is *not* to be construed as actual support
for GLSL shaders. The GL version is still 1.3, and stuff still sucks. Just
flicking it on so that it can be tested and developed a bit easier.

src/gallium/drivers/r300/r300_screen.c

@@ -88,8 +88,11 @@ static int r300_get_param(struct pipe_screen* pscreen, int param)
                 return 0;
             }
         case PIPE_CAP_GLSL:
-            /* IN THEORY */
-            return 0;
+            if (r300screen->caps->is_r500) {
+                return 1;
+            } else {
+                return 0;
+            }
         case PIPE_CAP_S3TC:
             /* IN THEORY */
             return 0;