Adding new API functions: register_id_with_basename, unregister_id_with_basename, find_ids_from_basename; adding test

This patch introduces the following new API functions:

 - register_id_with_basename, unregister_id_with_basename:  
 - find_ids_from_basename

all of which help to simplify orchestrating collective operations.

This patch also fixes an issue with the automatic conversion of a `hpx::naming::gid_type` which was returned by an action into a proper `hpx::id_type` instance.