lib-storage: Add reason to mailbox.transaction_begin()

Array API changed: ARRAY_DEFINE(name, type) -> ARRAY(type) name Easy way to update your existing code: perl -i -pe 's:ARRAY_DEFINE\(([^,]+), *([^)]+)\);:ARRAY($2) $1;:' **/*.[ch]

lib-storage: Removed struct index_transaction_context. All of its contents are now in struct mailbox_transaction_context.

index-storage: Simplified the way transactions are are created/finished. Removed also mail_storage.class_init/deinit since they're no longer used for anything. --HG-- branch : HEAD

virtual: Added support for saving/copying messages to virtual mailboxes. --HG-- branch : HEAD