mesa: Prefix main includes with dir to avoid conflicts.

Some of the headers in src/mesa/main have pretty common names which
easily conflict with third-party code, e.g. config.h
diff --git a/src/mesa/shader/arbprogparse.c b/src/mesa/shader/arbprogparse.c
index ff58335..78cc6aa 100644
--- a/src/mesa/shader/arbprogparse.c
+++ b/src/mesa/shader/arbprogparse.c
@@ -38,9 +38,9 @@
 #include "programopt.h"
 #include "prog_parameter.h"
 #include "prog_statevars.h"
-#include "context.h"
-#include "macros.h"
-#include "mtypes.h"
+#include "main/context.h"
+#include "main/macros.h"
+#include "main/mtypes.h"
 #include "prog_instruction.h"