I'm seeing an apparent side-effect of the new clean script (or it seems to correlate).  Since it started running, the Windows buildbots (both 7 and XP) seem to always perform a full clone of the master repository for each build rather than just a pull/update.  That's a noticeable performance difference (15-20 minutes per clone rather than the more typical 1-2 minutes for pull/update) and seems like it should be unnecessary.

I'm not quite sure how the buildbot task makes the decision between the two approaches, but could the new clean be removing a file that's relevant to how the decision is made?