another Makefile fix

[Stephen Weeks]

> > Here  is  another change that should be done to the relevant Makefile's (just
> > doc/web/Makefile at the moment, although bin/make-rpms  should  probably  get
> > this to): Test if CVSROOT is in the environment and fail, with an appropriate
> > complaint if it isn't.  Something like this:
> 
> Maybe, although I never set CVSROOT, because mlton is in one repository
> and at various other times, I've used other CVS repositories (e.g.,
> a local one for class projects).  So, I always do cvs -d... co ... and
> then the CVSROOT is kept in the corresponding CVS directories and I never
> need to enter it again.

I'm with Matthew -- that test is too brittle.  And I also point out again: no
Makefile uses cvs anymore.  The only use is in make-rpms.