The libssh2_init fix resolves the crash from #907. Calls to fetch would initialize openssh sessions in separate threads, and those would in turn call libssh2_init via https://github.com/libssh2/libssh2/blob/d441da3086dcc49989b7c5b9bf3043c4a6a98211/src/global.c#L74-L78 which is not thread-safe. Calling libssh2_init at app initialization makes sure it's initialized in a thread-safe way.

Providing openssl with the callbacks it needs to operate in a thread safe manner also seems to help, and is probably something we should be doing anyway.

There was a snag with doing the libssh2 initialization directly from nodegit.cc because node.h and libssh2.h had conflicting type definitions. The final fix for the problem was to move the libssh2.h include to a separate file and do the initialization from there.

LGTM