Get rid of warnings about using chars as subscripts
on Alpha (and possibly other platforms) by using Py_CHARMASK().
diff --git a/Modules/_tkinter.c b/Modules/_tkinter.c
index b85e158..ebaf799 100644
--- a/Modules/_tkinter.c
+++ b/Modules/_tkinter.c
@@ -647,7 +647,7 @@
 
 	strcpy(argv0, className);
 	if (isupper(Py_CHARMASK(argv0[0])))
-		argv0[0] = tolower(argv0[0]);
+		argv0[0] = tolower(Py_CHARMASK(argv0[0]));
 	Tcl_SetVar(v->interp, "argv0", argv0, TCL_GLOBAL_ONLY);
 	ckfree(argv0);