go/ast: fix ast.MergePackageFiles to collect infos about imports
go/ast: fix ast.MergePackageFiles to collect infos about imports

R=golang-dev, gri
CC=golang-dev
http://codereview.appspot.com/4710047

Committer: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang