- remove "localdune"-hack, not needed without lib

- add --enable-dunedevel which switches a define DUNE_DEVEL_MODE that
  in turn can be used to activate more output (will e.g. be used for
  exception output format)
- --with-dune works with both the directory above and the real
  dune-dir... if the directory is called "dune". Well, otherwise the
  includes won't work anyway :)

[[Imported from SVN: r713]]