Peter Chubb <peter@chubb.wattle.id.au>: make TAGS to work with bitkeeper:

  If you type, `make TAGS' in the top-level of a kernel tree that's been
  created with bk clone (or if you're using sccs to maintain your own
  copy), then the sccs control files are included in the TAGS file (sccs
  distinguishes its control files with an s. prefix rather than using a
  suffix, so the matches on '*.h' etc pick them up.)