[cvsnt] Detect a cvsnt vs cvs working copy?

[Stephen Kennedy]

> The 'updating' of formats that CVSNT does has no effect on the backwards compatibility with CVS, so there is no down side really (basically CVSNT adds some extra control files like CVS/Entries.Extra, which CVS 1.11 or 1.12 will just ignore).

Thanks, that's the point I was concerned about. It wouldn't do to
silently munge a working copy.
We'll just try cvsnt, cvs in that order.

Stephen.