Revert the order back to deleting then svn revert'ing, which is safer than the
reverse. Document a bit better the behavior.

R=dpranke@chromium.org
BUG=none
TEST=commit queue should die less often


Review URL: http://codereview.chromium.org/6681032

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@78224 0039d316-1c4b-4281-b951-d872f2087c98