This CVSROOT/ directory is only here to convince CVS that this is a
real repository.  Without it, CVS operations fail with an error like:

  cvs [checkout aborted]: .../main-cvsrepos/CVSROOT: No such file or directory

Of course, CVS doesn't seem to require that there actually be any
files in CVSROOT/, which kind of makes one wonder why it cares about
the directory at all.
