gssapi: Use *userok() functions only when authz_name != authn_name. Some more code cleanups.
gssapi: Use *userok() functions only when authz_name != authn_name.
Some more code cleanups.

--HG--
branch : HEAD

dscho/dovecot,dscho/dovecot,dscho/dovecot,dscho/dovecot,dscho/dovecot