feature/plural: pull in Form from internal plural package

Change-Id: Ib82046f65688dee8a244eaada03c6a9193856c5b
Reviewed-on: https://go-review.googlesource.com/39134
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>
7 files changed