use 'const char *' by default with RNA functions except when the value is flagged as PROP_THICK_WRAP.

Also use const char in many other parts of blenders code.

Currently this gives warnings for setting operator id, label and description since these are an exception and allocated beforehand.

source/blender/python/BPY_extern.h

@@ -126,7 +126,7 @@ extern "C" {
 	int BPY_eval_string(struct bContext *C, const char *expr);
 
 /* format importer hook */
-	int BPY_call_importloader( char *name );
+	int BPY_call_importloader(const char *name);
 //
 //	void BPY_spacescript_do_pywin_draw( struct SpaceScript *sc );
 //	void BPY_spacescript_do_pywin_event( struct SpaceScript *sc,