- add MailboxAliasConfig() and $called_by_MailboxHandler for special
handling if called by MailboxHandler
- create_allowed(): always allow creating an alias for a mailbox
- remove _missing_on_vacation() and _missing_active() which returned the
default from $this->struct. This is now done by default, see previous
change in PFAHandler
git-svn-id: https://svn.code.sf.net/p/postfixadmin/code/trunk@1424 a1433add-5e2c-0410-b055-b7f2511e0802