Cert checking now works correctly in both "SSLVerifyClient required" and "SSLVerifyClient optional" (authenticators do safety check themselves)

Providing certificates to HTTPSConnection was changed in Py 2.7.9, the old
way is still supported, but there is a memory leak (fixed in 2.7.12). The
code was changed to use the new way (SSLContext object) if it's
available, thus avoiding the leak.