- add_exclude() now takes a flag int and can optionally word-split

  items and/or ignore +/- prefixes.
- add_exclude_file() changed to take the same flags as add_exclude().
- add_exclude_line() was removed since add_exclude() can now do its job.
- make_exclude() now takes a size-limited string without a +/- prefix.
- add_cvs_excludes() was changed to word-split the items that come from
  a .cvsignore file, and to ignore all +/- prefixes in all the ignore
  sources.  Since CVS doesn't check if its ignore items are directories,
  the dir-names (e.g. SCCS, CVS, etc.) no longer have a trailing slash
  (making our excludes match CVS's ignores more exactly).