Fix gnutls session protocol detail setup.
Fix gnutls session protocol detail setup.

Don't set the details then immediately set them back to the defaults.
Complain if we can't set the various session options.
Complain if we can't set the session credentials.
Allow default options to be set via an environment variable.
Prio_cache storage not used anymore, using gnutls_priority_set_direct.

freedesktop-unofficial-mirror/wocky,noonien-d/wocky,noonien-d/wocky,freedesktop-unofficial-mirror/wocky,freedesktop-unofficial-mirror/wocky,noonien-d/wocky