Show the correct port number in the sieve-buffer's header

Fixed code to also work with a string as port specifier.
Make sieve-manage-open work with STARTTLS

Shorten stream managing functions in sieve-manage by using
open-protocol-stream to do most of the work.  Has the nice benefit of
enabling STARTTLS.
Remove unneeded functions and option

Delete the following functions, as they are neither in the API, nor
called by any other function:

* sieve-manage-network-p
* sieve-manage-network-open
* sieve-manage-starttls-p
* sieve-manage-starttls-open
* sieve-manage-forward

Delete options sieve-manage-streams and sieve-manage-stream-alist, as
those cannot be applied in a meaningful way; they didn't happen to have
much effect before, anyway.
Clean the sieve process buffer setup code

Split into separate function to make it clearer what's going on in the
code.
Enable Multibyte for SieveManage Buffers

Conflicts:
	lisp/sieve-manage.el
Replace while-loop with dolist in sieve-manage

Leads to ever so slightly nicer looking code.
Remove duplicate sieve keybinding for 'q'
Wait for answer before starting auth

Following RFC5804, the server sends new capabilities after successfully
establishing a TLS connection with the client.  The client should update
the cached list of capabilities, but we just ignore the answer for now.