refactor presubmit parsing code from git-cl into presubmit

This change moves the code I added to git-cl to parse the results of the presubmit hooks into presubmit_support itself. It also removes a lot of the text-file parsing that is no longer necessary since everything is in process.

It also simplifies all of the PresubmitResult* objects and the way we're using output streams since we can assume more about how the callers are calling us.

Note that I uses PEP-8 style method names where I was adding entirely new classes (or rewriting existing classes completely) since per maruel@ he is trying to new that style for new code.

This change also contains two small changes to git_cl to fix bugs and restore the previous behavior of --force skipping the presubmit checks.

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=78328

[chase, 2011-03-15 05:59:44]

lgtm

http://codereview.chromium.org/6694009/diff/1/tests/presubmit_unittest.py
File tests/presubmit_unittest.py (right):

http://codereview.chromium.org/6694009/diff/1/tests/presubmit_unittest.py#new...
tests/presubmit_unittest.py:602: 'Warning, no presubmit.py found.\n'
indent +1

[M-A Ruel, 2011-03-15 13:40:57]

lgtm

[Dirk Pranke, 2011-03-16 01:00:44]

I backported the --force change and the other git-cl fix from the gcl change to
this patch, because git-cl would've broken otherwise.

[chase, 2011-03-16 02:03:00]

lgtm