Rewrite of `drupal-detect-drupal-version' needed

The use of dir-locals (`dir-locals-set-class-variables' and `dir-locals-set-directory-class' in `drupal-detect-drupal-version' has proved not to be an ideal solution.

The "project local" variables is not always set correctly resulting in some buffers not entering drupal-mode and/or not having drupal-rootdir set. This limits usabilty of drupal-mode a lot.

We have to redo the handling of the project local variables. And a cleanup of the detection and parsing of drupal-rootdir, drupal-version, etc. could also be a good idea.