option to use external program for opening UDP sockets

[ibukanov]

Currently mosh client does not support UDP proxies preventing to use it from some corporate networks. It also does not support using a different port when reconnection to a server which may be required when switching between internal and external network.

All this can be addressed if the mosh-client to reconnect could use an external program that opens UDP connection to the server and passes the resulting socket back to moch-client. Then such proxy can implement port change, connecting via SOCKS5 proxy etc.

This will be similar to the ProxyUseFdpass option to ssh, http://www.gossamer-threads.com/lists/openssh/dev/56016#56016

[m0yellow]

USB Sockets, maybe UDP Sockets?

This would allow funky connect scripts ....

[achernya]

This probably would benefit from #431