Anyone know of a version of patch(1) that can do a cvs-savvy 3-way merge?

[Darin Adler <darin bentspoon com>]

I was thinking recently that old patches often have the version numbers they
were diff'd with, if the patches were made with cvs diff. Those patches
could be applied much better by a cvs patch tool that got the old versions
in question and did a 3-way merge, the way cvs normally does. That could be
a time saver when applying an old patch from bugzilla to prepare it for
check-in.

I can also do this by hand, but it would be way nicer to tie these together.

Does anyone know of an existing tool like this? I'd like to find it before I
roll my own.

    -- Darin