go/build: include Import objects in Script Inputs
go/build: include Import objects in Script Inputs

This has the effect of making goinstall rebuild a package's
dependencies when they are newer than the current package object.

R=rsc
CC=golang-dev
http://codereview.appspot.com/4627051

tav/go,tav/go,tav/go,tav/go,tav/go,tav/go,tav/go