cmd/go: avoid infinite loop with package specific flags
cmd/go: avoid infinite loop with package specific flags

R=rsc
CC=golang-dev
http://codereview.appspot.com/5505053

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