src/cmd: Add a repurposed import(4), called `9import', to the ports. The code is adapted from Plan 9's import(4); this allows us to speak that protocol. We don't currently support AAN (in the works) or TLS/SSL. Thanks to David for help with the man page, testing, and development. R=0intro, rsc CC=plan9port.codebot http://codereview.appspot.com/6458100