Patch by Andreas Schulze.

This allows performing ManageSieve actions at command line or through doveadm server.

Change backported from Pigeonhole v0.4 tree, which means that this change will duplicate there upon merge.

sieve-refilter: improved man page documentation by explicitly specifying the syntax used for mailbox arguments.

- Now compiles regularly without --with-unfinished-features
- Still experimental though, so be careful.
- Changed command structure a bit, removing the useless -M option.

Made vnd.dovecot.debug extension available to the LDA plugin instead of only the command line tools.

- No longer track the generated pigeonhole.7
- Some makes don't like the 'handy' notation that was used.
- Deleted trailing spaces
- Escaped some dashes
- Replaced some ' and " by \(aq and \(dq
- Sorted manual pages in section 'See also'
  (first list all man pages from the lowest section (1)
  alphabetical sorted, then the next section …)