Make build_nexe.py rebuild when script itself has changed.
Make build_nexe.py rebuild when script itself has changed.

BUG=http://code.google.com/p/chromium/issues/detail?id=391093
TEST=trybots, null build ok, touch build_nexe.py rebuilts all, touch source rebuilds.
R=mseaborn@chromium.org

Review URL: https://codereview.chromium.org/378513006

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@13520 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client