Remove bareword fallback for constants

Access to undefined constants will now always result in an Error
exception being thrown.

This required quite a few test changes, because there were many
buggy tests that unintentionally used bareword fallback in combination
with error suppression.

Zend/zend_constants.c

@@ -424,7 +424,7 @@ failure:
 			return &c->value;
 		}
 
-		if (!(flags & IS_CONSTANT_UNQUALIFIED)) {
+		if (!(flags & IS_CONSTANT_UNQUALIFIED_IN_NAMESPACE)) {
 			return NULL;
 		}