lib-storage & imap: add MAIL_ERROR_UNAVAILABLE as [UNAVAILABLE] [UNAVAILABLE] is defined in RFC 5530 and we were just missing a MAIL_ERROR_* constant to make use of it.

lib-storage: Add explicit MAIL_ERROR_LOOKUP_ABORT error The MAIL_ERROR_NOTPOSSIBLE was a bit too generic to assume to mean the same thing. It doesn't look like there are any external plugins that break because of this change.

lib-storage: Add MAIL_ERROR_LIMIT

lib-storage: remove obsolete constants

Compiling fix for previous change..

Handle "out of disk space" and "out of user quota" as separate cases. "Out of disk space" is a temporary error that should be logged as error and the failure should be sent to user as "Internal server error". Obsolete the use of MAIL_ERROR_NOSPACE and MAIL_ERRSTR_NO_SPACE. Use the clearer MAIL_ERROR_NOQUOTA and MAIL_ERRSTR_NO_QUOTA instead.

imap: Fixed handling FETCH BINARY for broken content.

IMAP BINARY extension supports now FETCH BINARY command.

Permission denied error handling can now suggest missing +w permissions. --HG-- branch : HEAD

Improved "Permission denied" error handling. It'll now show also the uid/gid name. Also moved the code to mail-error.c and used it when listing mailboxes. --HG-- branch : HEAD

Made CRITICAL_MSG* public to MAIL_ERRSTR_CRITICAL_MSG* in mail-error.h. --HG-- branch : HEAD

Implemented imap-response-codes draft. --HG-- branch : HEAD

Changed .h ifdef/defines to use <NAME>_H format. --HG-- branch : HEAD

Added MAIL_ERROR_EXPUNGED. Set the error whenever expunged message is tried to be accessed. --HG-- branch : HEAD

Error handling rewrite. --HG-- branch : HEAD