httplib_connect_client_impl is not thread safe

[lammertb]

This function uses a fake ctx structure which is static and returned in the connection if this function returns. So technically there can only run one client connection at the time.

[lammertb]

I am now actually quite sure that this is a severe bug. When running SSL, the client SSL context is linked to the fake context and this context can than be reused by different connections. This is not only a threading issue, but also a security issue. The only solution is that each connection where LibHTTP functions as the client has its own context.

[lammertb]

Fixed in f5e4015 which now mandates that the calling application provides a proper client context.