Export Google-internal library

Exporting the Google-internal CAP library as submitted at HEAD. Also, fixing the CAP validator to be compatible with it.

The new CAP library has a bunch of new features, bug fixes and validation heuristics. More details to follow in the notes of the upcoming release.
"The whole thing" meaning the validator?  The validator does have some code that tries to send mail, maybe that's the issue.  I don't recall ever seeing errors when I added that though.

If it is the validator, I'd rather this dep appear in a separate MANIFEST under validator/
If it isn't the validator, then I'll have to dig in deeper.