LP#1488655: fix MR remapping upon fingerprint change

LP#1488655: fix MR remapping upon fingerprint change

This patch ensures that if the fingerprint of a bib changes, the
bib will be moved to a new metarecord as opposed to ending up
as a member of more than one metarecord.

To test
-------
[1] Note the metarecord that a bib belongs to.
[2] Change the bib so that its fingerprint changes -- with stock
    cbf settings, editing the 245$a should suffice.
[3] Note that it is now a component of two metarecords.
[4] Apply the patch.
[5] Repeat step 2 or force a reingest. The bib should now be part
    of exactly one metarecord.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>