Encapsulate reference-counting primitives.

Prohibit direct update of GC_REFCOUNT(), GC_SET_REFCOUNT(), GC_ADDREF() and GC_DELREF() shoukf be instead.
Added mactros to validate reference-counting (disabled for now).
These macros are going to be used to eliminate race-condintions during reference-counting on data shared between threads.

ext/intl/common/common_enum.cpp

@@ -183,7 +183,7 @@ static zend_object_iterator *IntlIterator_get_iterator(
 		return NULL;
 	}
 
-	++GC_REFCOUNT(&ii->iterator->std);
+	GC_ADDREF(&ii->iterator->std);
 
 	return ii->iterator;
 }