Implement accelerated tee support for POSIX.

Implement accelerated tee support for POSIX.

This removes all the need of threading, which removes the contention on the GIL
lock.

Taking S2Test.test_check_output_tee_large as baseline, numbers are
real/user/sys in seconds:
Ubuntu workstation: ~25x  2.4/1.9/1.5 -> 0.10/0.70/0.02
OSX 10.6 laptop:    ~40x  6.4/5.3/3.9 -> 0.15/0.80/0.07
Cygwin on win7:      ~4x  2.8/2.2/1.3 -> 0.60/0.16/0.30

R=dpranke@chromium.org
BUG=
TEST=


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=109283

[Dirk Pranke, 2011-11-09 03:47:35]

lgtm

[commit-bot: I haz the power, 2011-11-09 19:24:59]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/maruel@chromium.org/8462008/3001

[commit-bot: I haz the power, 2011-11-09 19:30:58]

Change committed as 109283