Don't block execution.

Python 2.4 has been untested for a while and may break unexpectedly.

TEST=manual testing
BUG=none

Review URL: http://codereview.chromium.org/5110009

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@66870 0039d316-1c4b-4281-b951-d872f2087c98