Change name of Changeset.java -> ChangeSet.java to fix compilation on
unix.

Note that checking this commit out on Windows may be troublesome, as for
Windows the name doesn't change. It might thus be needed to name the
file and then recreate it with the checkout command. Failing that,
removing the fail and issuing the reset command with the --hard flag
should do it. Be careful though, as that resets *all* files in the
repository.