Show a list of directories missing OWNER reviewers on upload, and show directories rather than files missing OWNER approvals on commit.

BUG=117166
TEST=covered by presubmit unittests

Review URL: http://codereview.chromium.org/9621012

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@125588 0039d316-1c4b-4281-b951-d872f2087c98