Fix generator to cope with call-by-ref long types

Fix generator to cope with call-by-ref long types

From: Matthias Bolte <matthias.bolte@googlemail.com>
Tested-by: Jim Fehlig <jfehlig@novell.com>
Matthias provided this patch to fix an issue I encountered in the
generator with APIs containing call-by-ref long type, e.g.

int virDomainMigrateGetMaxSpeed(virDomainPtr domain,
                                unsigned long *bandwidth,
                                unsigned int flags);