Now that go/types permits files to be added to a package
incrementally (fixing bug 7114), this CL extends the loader
to load and augment multiple test packages at once.
TESTED:
- go/loader/stdlib_test runs the type-checker on the entire
standard library loaded from source in a single gulp, with
each package augmented by tests.
- Manually tested on:
% ssadump -test -run unicode encoding/ascii85
Both sets of tests are run (and pass).
LGTM=gri
R=gri
CC=golang-codereviews
https://golang.org/cl/61060043
Alan Donovan