BibConvert: oaiarXiv to MARCXML updates
BibConvert: oaiarXiv to MARCXML updates

* Fixes an issue with duplicate 690C_$$aCERN and 980__$$aCERN
  when converting records from oaiarXiv format to MARCXML.

* Removes some erroneous output in converted MARCXML.

* Also replaces tabs with spaces.

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