Because the std go/importer's Lookup functionality is incomplete,
clients have no way to create a Go 1.5 types.Package from an io.Reader
reading from gc export data. This package provides a stopgap until
the standard library is complete.
The go/gcimporter package remains unchanged, and uses only the
golang.org/x/tools/go/types package.
Change-Id: I47a817f4b6a52ddab26c6b01de6e28099301faf5
Reviewed-on: https://go-review.googlesource.com/18382
Reviewed-by: Robert Griesemer <gri@golang.org>