2012-08-16 17:34 AEST by Arthur Barrett - If a particular user connects (e.g.: as anonymous user cvs) with an old client, then it may be necessary to 
prevent access.

This can't be done as a 'traditional' warning because the client may not recognize the error (e.g.: WMFree). 

If the operation is 'rls' (or the equivalent 'co') then we should just list a single 'file':
'Please upgrade your client software.txt'

Checkout could 'checkout' the same file, or a pre-defined file/revision defined in the configuration file.

The 'info' commands (enum protocol) should be allowed

All other operations (tag, ci, admin, update, diff) should simply fail.