John McEleney / mailutils

(_address_get_nth): Get nth sub-address from an address.

(most of the functions): Rewritten using _address_get_nth
(address_aget_personal, address_aget_comments): new functions.
(address_dup): New function. Create a copy of a (single) address.
(address_contains_email): New function. Check if the given email
is contained in the address.
(address_union): New function. Create a union of two addresses.