[Groff] name clashings

[Bernd Warken]

As was discussed in a different thread, there is a danger of
inadvertently overwriting existing system names when defining
macros, strings, etc.

So some mechanism should be filed on the TODO list that helps to
avoid this situation.

I could imagine an optional warning facility.  All name clashings
are warned; to overwrite an existing name, it must be explicitly
deleted.

Bernd Warken