Always use an SSL context. [Fixes #548]

This reverts commit 9890b197c51f1d340fa7275aa4bc17103746657b, as latest
patch releases of 1.8.7 do accept an OpenSSL context object.

This has been broken since the refactoring d6e25e5e37e6d591f94cc04a2a52c1128fde81db,
which increased the scope of the original breakage.