the root of the source tree. It is similar to "gclient diff", and
shares much of the implementation, but it seems that developers may
want the semantics of each in different situations, which is why it is
being added as a new command.

Generalized SubprocessCallAndCapture into SubprocessCallAndFilter.
Added RunSVNAndFilterOutput; changed RunSVNAndGetFileList to use it.
Fixed problem in presubmit_canned_checks.py where it was not working
on Windows. Updated unit tests for gclient.

Review URL: http://codereview.chromium.org/193004

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@25410 0039d316-1c4b-4281-b951-d872f2087c98