mosh: use brewed openssl as default

The openssl library bundled with OS X operation system is deprecated. It is better to link against the brewed openssl library instead of the system one.

In addition the option to link against the system one is offered.
emm, we have the perl script  ``mosh`` and two binary files ``mosh-client``, ``mosh-server``. I believe the runtime check need networks. Ahh, maybe we can run mosh-server in daemon and then spawn a new mosh-client process to connect it