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/windowmanager/intern/wm_files.c

@@ -262,7 +262,7 @@ static void wm_init_userdef(bContext *C)
 	if(U.tempdir[0]) BLI_where_is_temp(btempdir, 1);
 }
 
-void WM_read_file(bContext *C, char *name, ReportList *reports)
+void WM_read_file(bContext *C, const char *name, ReportList *reports)
 {
 	int retval;