Keep directory in working tree, but exclude from foo.diff.gz

[Ben Finney <ben@benfinney.id.au>]

Howdy mentors,

I have a working tree for a package that's under version control; the
working tree is specific to the Debian packaging for the software.

That working tree contains a (version-controlled) directory that must
remain in the working tree, and remain under version control, but
should *not* become part of the Debian foo.diff.gz against the
upstream source. The directory contains developer-only data that is
not part of the Debian package, but *is* part of the data that should
be under VCS in that working tree.

So, in this case, it's not appropriate to have the directory removed
by the 'debian/rules clean' action; the files need to remain in the
working tree.

What would be the best way to keep such a directory in place, but
exclude the directory from the Debian source and binary packages?

-- 
 \      "If you can do no good, at least do no harm."  -- _Slapstick_, |
  `\                                                     Kurt Vonnegut |
_o__)                                                                  |
Ben Finney