go.tools/go/types: enable std lib test of map key types
go.tools/go/types: enable std lib test of map key types

R=adonovan
CC=golang-dev
https://codereview.appspot.com/17390043

karmakaze/go.tools,lattera/go.tools,chenjianlong/go.tools,lattera/go.tools,lattera/go.tools,karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools,chenjianlong/go.tools,karmakaze/go.tools,chenjianlong/go.tools