Disable SSLv3 unconditionally. Closes ticket 13426.

The POODLE attack doesn't affect Tor, but there's no reason to tempt
fate: SSLv3 isn't going to get any better.
Merge branch 'no_sslv3_023' into maint-0.2.3
Merge remote-tracking branch 'origin/maint-0.2.3' into maint-0.2.4