Make MAIL_INDEX_MAIL_FLAG_BACKEND visible to mail_get_flags() and allow it to be changed.
Make MAIL_INDEX_MAIL_FLAG_BACKEND visible to mail_get_flags() and allow it
to be changed.

LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot