- Moved `dist' rule that sets up SRC_DIST_FILES symlinks past
  the recursive `dist' rule that creates the shadow dist tree.
- Experimental support for aliases in SRC_DIST_FILES lists, i.e.,
  foo~bar will create a symlink from `bar' in the dist tree to
  `foo' in the build tree (useful for the cases where you're
  shipping Makefiles that differ from the fptools/ ones.)
- New target `dist-manifest': create MANIFEST files for a
  (source) distribution.