bug #504 fix

bug #504 fix
The GRS module now ignores any previously existing GRS subtree of the form
  <idzebra xmlns="http://www.indexdata.dk/zebra/">
    ...
  </idzebra>
both under indexing and retrieval of records. This is to facilitate remote
update of GRS records, which have been augmented by zebra-internal meta data
info, such that this part is not appended twice.
   The local storage is still including the GRS <idzebra ..> subtree, but
it is not indexed any more, and stripped before retrieval, i.e. for all
practical purposes it is not existent.