check for assignment to __debug__ during AST generation

Also, give assignment to None a better error message
diff --git a/Python/ast.c b/Python/ast.c
index 29b0e82..6eb3aa4 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -130,7 +130,9 @@
 forbidden_check(struct compiling *c, const node *n, const char *x)
 {
     if (!strcmp(x, "None"))
-        return ast_error(n, "assignment to None");
+        return ast_error(n, "cannot assign to None");
+    if (!strcmp(x, "__debug__"))
+        return ast_error(n, "cannot assign to __debug__");
     if (Py_Py3kWarningFlag) {
         if (!(strcmp(x, "True") && strcmp(x, "False")) &&
             !ast_warn(c, n, "assignment to True or False is forbidden in 3.x"))
diff --git a/Python/compile.c b/Python/compile.c
index 264fdcd..88d54ab 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -2344,12 +2344,6 @@
 	PyObject *mangled;
 	/* XXX AugStore isn't used anywhere! */
 
-	/* First check for assignment to __debug__. Param? */
-	if ((ctx == Store || ctx == AugStore || ctx == Del)
-	    && !strcmp(PyString_AS_STRING(name), "__debug__")) {
-		return compiler_error(c, "can not assign to __debug__");
-	}
-
 	mangled = _Py_Mangle(c->u->u_private, name);
 	if (!mangled)
 		return 0;