go spec: receiver, parameter, and result names must always be unique
go spec: receiver, parameter, and result names must always be unique

Fixes issue 4450.

R=rsc, iant
CC=golang-dev
https://codereview.appspot.com/6845104

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