syscall: add a test for passing an fd over a unix socket
syscall: add a test for passing an fd over a unix socket

Updates issue 1101

R=golang-dev, iant
CC=golang-dev
http://codereview.appspot.com/5849057

dsriram/golang,pombredanne/go-deleteme,apparentlymart/golang,gnanderson/go,tv42/old-go,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,tv42/old-go,pombredanne/go-deleteme,gnanderson/go,gnanderson/go,tv42/old-go,apparentlymart/golang,gnanderson/go,pombredanne/go-deleteme,tv42/old-go,gnanderson/go,dsriram/golang,pombredanne/go-deleteme,dsriram/golang,pombredanne/go-deleteme,apparentlymart/golang,dsriram/golang,pombredanne/go-deleteme,tv42/old-go,dsriram/golang,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,gnanderson/go,dsriram/golang,dsriram/golang,gnanderson/go