mdbox: Added "mdbox_deleted" storage, which can be used to access messages with refcount=0 For example: doveadm import mdbox_deleted:~/mdbox "" mailbox inbox subject oops

mdbox: Moving messages to alt storage is done done with doveadm altmove command. The command can take an arbitrary search query listing what messages should exist in alt storage. If the message has been copied to multiple mailboxes, the search query must match all the instances of the message. Since the search query can now be specified in command line, mdbox_altmove setting was also removed. --HG-- branch : HEAD

dbox: Use flock() for file locking if possible. If not, require client_limit=1. Maybe some day dbox code can be redesigned in a way that allows it to work with fcntl() locking too. --HG-- branch : HEAD

configure: Removed --enable-header-install. It's now always enabled. There didn't seem to be much point in keeping it optional anymore. They're now more useful than before because shared libraries are also installed. --HG-- branch : HEAD

Split dbox (single-dbox) and mdbox (multi-dbox) into separate storage backends. This cleans up the code, makes it faster and also fixes some bugs. Super-fast maildir migration code was also dropped, at least for now. --HG-- branch : HEAD