Allow cvs export without tag

[Spiro Trikaliotis]

Hello,

the attached (mini-)patch allows to give a revision with "cvs export
-r". Currently, only symbolic tags are allowed.

If the user specifies a revision with export, a warning is printed, but
the export is not aborted. Currently, an error is output and the export
is rejected.

The patch applies upon HEAD.

I hope I did all correct and you do not reject it. :) Of course, if you
want any "fixes", I will happily make them.

Thank you,
   Spiro.

-- 
Spiro R. Trikaliotis                              http://cbm4win.sf.net/
http://www.trikaliotis.net/                     http://www.viceteam.org/