VERP_SEPARATOR replacement (and re-subscribe bug?)

attached are two patch files to add customized VERP_SEPARATORs to email addresses. This is needed when MTAs other than postfix are used (in particular, for qmail).

While the email address is formed correctly now for the re-subscribe (after a successful unsubscribe request) I'm not getting a successful resubscribe. Perhaps a code is missing indicating who should be re-subscribed to which group:

subscribe-1-4@testing.civicactions.net

(the "subscribe-1-4" seems a little short and suspect...)