[Patch] Allow for more than one recipient_delimiter (a la postfix 2.11)

Hey everyone,

as my previous emails apparently got stuck in a spam filter I'll try this again. The patches attached here allow for more than one recipient delimiter in the address. Which is allowed in postfix since version 2.11. E.g. lhw+postfix@ring0.de would be equal to lhw-postfix@ring0.de if configured that way. Same as postfix only the first discovered delimiter is taken into account and the priority is first to last in the list.

Lennart