I suspect this is because my PATH was getting too long within my build script because of setting up the VS build environment too many times (if PATH gets too long then new processes may ignore or truncate it).

The commit should cut this down to the point where we don't lose Mercurial off of PATH, but I'm running validation builds to be sure.

As this only applies to the Windows builds and we haven't seen it against 3.5 yet, I'm dropping that from the versions list.