BibMerge: delete cache file on submit
BibMerge: delete cache file on submit

* On submit, delete the cache file so that the record can be
  reopened, e.g with BibEdit.

Reviewed-by: Tibor Simko <c7116e45300b163846dc01f3ed02116e3f8ef7a5@cern.ch>

inveniosoftware/invenio,inveniosoftware/invenio,tiborsimko/invenio,tiborsimko/invenio