R1:8269fd6e6c1f

Decode "Content-Encoding: gzip" content

Summary:
Fixes T10228. When we receive a gzipped request (rare, but `git` may send them), decode it before providing it to the application.

This fixes the issue with proxying certain requests described in T10228.

Test Plan:
- Applied this fix in production.
- Cloned a problem repository cleanly.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10228

Differential Revision: https://secure.phabricator.com/D15145