We now return the stderr half of the tuple.
This required a clean up of any usage of CheckCall and GIT.Capture.

Patch contributed by Nasser Grainawi <nasser@codeaurora.org>

Review URL: http://codereview.chromium.org/551215

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@37650 0039d316-1c4b-4281-b951-d872f2087c98