Don't know about hg, but `cvs up -dP' gets it done on case-
INsensitive HFS+ volumes on Macs I have.  Source sync tool of
preference aside, I can second rog on case- sensitive HFS (or
even Mac(NeXT) UFS if you like). Since both of these can be less
convenient on boot volumes, a partition for the purpose, or a
removable of some kind so formatted, is handy, since the
filename case issue comes up in more than just p9p.