Disable SSLv3 (in favor of TLS) for the RPC client and server.

TLS is subject to downgrade attacks when SSLv3 is available, and
SSLv3 has vulnerabilities.

The popular solution is to disable SSLv3. On the web this breaks
some tiny number of very old clients. While Bitcoin RPC shouldn't
be exposed to the open Internet, it also shouldn't be exposed to
really old SSL implementations, so it shouldn't be a major issue
for us to disable SSLv3.

There is more information on the downgrade attacks and disabling
SSLv3 at https://disablessl3.com/ .