gc: improve error message for x \= 0
gc: improve error message for x \= 0

was
x.go:2: syntax error: unexpected $undefined

now
x.go:2: syntax error: unexpected \

R=ken2
CC=golang-dev
http://codereview.appspot.com/2267044
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go