go.tools/ssa/interp: enable $GOROOT/test/switch.go test
go.tools/ssa/interp: enable $GOROOT/test/switch.go test

(now that go/types can handle it)

R=gri
TBR=gri
CC=golang-dev
https://codereview.appspot.com/16970043

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