go.tools/importer: retain scope information.
go.tools/importer: retain scope information.

(It's needed by the oracle.)

R=crawshaw, gri
CC=golang-dev
https://codereview.appspot.com/13071043

tmc/mirror-go.tools,t-yuki/go.tools.old,t-yuki/go.tools.old,t-yuki/go.tools.old,tmc/mirror-go.tools,tmc/mirror-go.tools