go/parser: better error sync. if commas are missing
go/parser: better error sync. if commas are missing

This time for sure.
Runs all tests.

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/5752060

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