workaround for boost 1.53 TLS 1.2

[iamthebot]

Fixes compilation issue since Boost 1.53 doesn't have a TLS v1.2 SSL context. So we trick it by setting the OpenSSL flags directly.

[eidheim]

Thank you, but I think it would be better to create the workaround through preprocessor #if ... #else ... #endif. There is probably a boost preprocessor definition for the currently used boost version.

The reason why is that it makes it clear that this is a workaround for older boost versions and that we can remove the preprocessor checks in the future.

[iamthebot]

@eidheim I've tested this refactored version in production and it's working reliably. We use cmake's detection of the boost version to use a fallback codepath (via a macro) for forcing TLS 1.2 ciphers. The normal codepath is unchanged.

Let me know if this works so it can be merged in.

[eidheim]

Thank you, and sorry for the late reply. However, I'm thinking that we could determine the boost version based on an already defined boost macro. See for insance here: http://stackoverflow.com/questions/3708706/how-to-determine-the-boost-version-on-a-system