Take two at r102841.

Forgot to use $base_dir, so the .pyc files in the checkout were deleted, instead
of the ones in depot_tools. Since some slaves have very large checkouts, they
appeared as hung.

R=cmp@chromium.org
BUG=
TEST=


Review URL: http://codereview.chromium.org/8059001

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@103056 0039d316-1c4b-4281-b951-d872f2087c98