Removing already completed items from future completions?

[Wayne Davison <wayned@xxxxxxxxxxxxxxxxxxxxx>]

It sure would be nice if a completer could be made to remove items that
had already been inserted into the command-line.  For instance, in the
completion for cvs: if I type "cvs commit <I>", and it mentions "foo"
and "bar", I'd sure love it if "cvs commit foo <I>" would just insert
"bar" (since "foo" would have been omitted from the list).

..wayne..