added another check to MARC framework test

added another check to MARC framework test

Check verifies that all subfields for each tag
are assigned to the same editor tab (or are ignored).

This situation can lead to data corruption, because
if an incoming MARC record has a field whose subfields
are assigned to different tabs, the first time that
record is saved in the bib editor, the field
will be split into multiple versions, each containing
the subfields assigned to a given tab.

Errors identified by this test known
in the MARC21 frameworks - I'm working on a patch to
correct those.

Signed-off-by: Joshua Ferraro <jmf@liblime.com>