doveadm: Add open read-only parameter to mailbox iterator This allows iterating mailboxes so that they are opened for read-only.

doveadm_mail_iter_init(): Removed unnecessarily returning transaction. If it's needed in future just add a new doveadm_mail_iter_get_transaction().

Removed all the "enum foo;" declarations. They didn't seem to be very standard. Old gcc versions warn about them and C++ code doesn't like them.

Marked functions parameters that are allowed to be NULL. Some APIs were also changed. The non-obvious APIs where NULL parameter was changed to "" are master_service_init() and auth_master_user_list_init(). These checks can currently be enabled only on a patched clang: http://llvm.org/bugs/show_bug.cgi?id=6786

doveadm expunge: Added -d parameter to delete mailbox if it's empty after expunging.

doveadm: Improved error handling. Failures should now always have non-zero exit code. doveadm now uses sysexits.h exit codes in most places, although there are still a lot of places where it simply returns EX_TEMPFAIL even though something else might be better.

doveadm: doveadm_mail_iter_init() API change to fix "doveadm fetch" crash.

lib-storage: Changed mailbox_search_*() API to return pointer struct mail. This reduces the flexibility, because now different mailbox_search_next() calls can't have different mail parameters with possibly different wanted_fields settings. This flexibility was never used though, and removing it gives a couple of benefits: * it's now easier for backends to implement prefetch and parallel search * usage is easier since mail_alloc()/mail_free() is no longer needed

doveadm: Added "move" command for moving mails between mailboxes.

doveadm altmove: Sync all mailboxes after moving mails. --HG-- branch : HEAD

doveadm: Removed more code duplication from altmove/fetch commands. --HG-- branch : HEAD