added support for parentGUID

added support for parentGUID

This is made up of 4 parts:

  1) change our schema to include the parentGUID attribute type

  2) in the add hook in the objectclass module, get the objectGUID of
  the parent and add it to the message as parentGUID

  3) in the rename hook in the objectclass module, get the objectGUID
  of the new parent, and insert an async modify request after the
  renmam is done

  4) added a simple test suite