http2: mix cleanups, TODOs, new tests, enforce header list size in Transport

Just re-reading the code and polishing things up.

Nothing major. Enforcing the max header list size in the Transport and
letting it be configurable (not exposed in Go 1.6, only via x/net) is
the most notable. Mostly just tests.

Change-Id: Iacbad5a0b1ba0df9296b1aecfbc8b9b83323d435
Reviewed-on: https://go-review.googlesource.com/18367
Reviewed-by: Blake Mizerany <blake.mizerany@gmail.com>
3 files changed