Fix https connections over a proxy

Fixes: https://bugzilla.osafoundation.org/show_bug.cgi?id=13049
Fix S/MIME documentation and examples

Fixes: https://bugzilla.osafoundation.org/show_bug.cgi?id=13020
Allow overriding SSL.Connection.postConnectionCheck

Fixes: https://bugzilla.osafoundation.org/show_bug.cgi?id=12973