Support Ruby 1.9.3

[Sharpie]

SSL connection tracing is currently implemented via TracePoint which is only present on Ruby 2.0 and newer. Ruby 1.9.3 could be supported by creating an alternate implementation based on set_trace_func.

[Sharpie]

After poking around a bit, this may actually be difficult to do.

One nice thing about TracePoint, aside from being able to declare multiple instances, is that the current object is available via the tp.self method. On the other hand, set_trace_func only exposes the current binding. Since SSLSocket#connect is a C method, there doesn't seem to be a way of acquiring a reference to the socket that connected via the binding :(

[Sharpie]

One thought: Fall back to monkeypatching.

Instead of trying to make set_trace_point work, just re-factor the SSLkeylog::OpenSSL module so that it can be included by OpenSSL::SSLSocket in a way that overrides the connect method. This sort of approach won't be targetable or reversible, but may be "good enough" for 1.9.3.