Fix transparent gzip for basic auth.

Externally reported Android bug:
https://code.google.com/p/android/issues/detail?id=74026

Thanks to mattpan91 for the report.

The issue was fixed in OkHttp 2.0. It has now been back-ported to 1.6.

This is a cherry pick from the okhttp_16 branch:
https://github.com/square/okhttp/commit/e8fee51087a062384f52e11400ff4a104a00a2b2

The merge was not entirely straightforward: Android is currently not quite
on 1.6; it is close and it was only the package for the files that differed
for existing files. There is an additional class (Job) that had to be patched
that the version Android has and 1.6 does not have. The class is probably not
used on Android.

The okhttp CTS tests pass, modulo some tests known to be flaky.

Bug: 16628050
Bug: https://code.google.com/p/android/issues/detail?id=74026

(cherry picked from commit f6af62d5)

Change-Id: I3172789a17384666eba732a7782573e08f06a48c