support for path alias chains in drupal_get_path_alias.

This is a small patch for function drupal_get_path_alias in bootstrap.inc.

This allows a path to have a non-cyclic chain of aliases, and enables the path alias finder to walk up the chain to the top level alias.

For example:

taxonomy_menu/4/1/50 | topics/whats_new/events
taxonomy/term/50 | taxonomy_menu/4/1/50

Now I can have all references to taxonomy/term/50 automatically point to the top-level alias, topics/whats_new/events.

I am also posting a patch against Pathauto module which creates these multi-links automatically for categories when taxonomy_menu is present. (I will add followup with a link to that patch).

Note that the inverse case (alias => path) is *not* necessary (in fact it would break the intention of this patch...

---

There are several other ways to accomplish this; all of which are more involved. YMMV. I won't be insulted if this patch is rejected. :)

An alternative solution would be to allow the destination column to accept non-unique entries. This would also require some sort of weighting otherwise the final resolution would be indefinate.

A second alternative would be to have drupal generate taxonomy links in a more general manner, so that the taxonomy_menu module could change all the taxonomy links via the proper hooks.

A *third* alternative would be to fix the menu system so that it does not require nested paths in the hiearchy, this way taxonomy_menu would not need to create its own paths.