gc: fix use of typekind array in error messages
gc: fix use of typekind array in error messages

Fixes issue 1697.

R=ken2
CC=golang-dev
http://codereview.appspot.com/4395045
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go