Thanks to Andrey Mirtchovski for tracking this down.

This was broken by CL 5528077 which removed the InsertSemis
flag from go/scanner - as a result, semicolons are now always
inserted and the respective indexer code checked for the
wrong token.

Replaced the code by a direct identifier test.

R=rsc
CC=golang-dev
https://golang.org/cl/5606065