Fix domain reference leaks

Fix domain reference leaks

Besides two unlikely/rarely hit ones in x86 code, the main offender
was tmh_client_from_cli_id(), which didn't even have a counterpart
(albeit it had a comment correctly saying that it causes d->refcnt to
get incremented). Unfortunately(?) this required a bit of code
restructuring (as I needed to change the code anyway, I also fixed
a couple os missing bounds checks which would sooner or later be
reported as security vulnerabilities), so I would hope Dan could give
it his blessing before it gets applied.

Signed-off-by: Jan Beulich <jbeulich@novell.com>