OpenSSL: Fix forcing SSLv3 connections

Some feedback provided by byte_bucket on IRC pointed out that commit
db11750cfa5b1 wasn’t really correct because it allows for “upgrading” to a
newer protocol when it should be only allowing for SSLv3.

This change fixes that.

When SSLv3 connection is forced, don't allow SSL negotiations for newer
versions.  Feedback provided by byte_bucket in #curl.  This behavior is
also consistent with the other force flags like --tlsv1.1 which doesn't
allow for TLSv1.2 negotiation, etc

Feedback-by: byte_bucket
Bug: http://curl.haxx.se/bug/view.cgi?id=1319