bug_6210: Select framework if merging two records with different frameworks

bug_6210: Select framework if merging two records with different frameworks

ModBiblio() - set framework to "" if "Default"

Signed-off-by: Nicole C. Engard <nengard@bywatersolutions.com>
All 4 tests passed:

Test 1:  Merge two records with the same framework
    Desired result:  shouldn't get any prompting to pick a framework, and the
same framework should be used

    Test 2:  2 records, different frameworks, into the kept record's framework
    Desired result:  merge with kept records framework used

    Test 3:  2 records, different frameworks, into the discarded record's
framework
    Desired result:  merge with used records framework used

    Test 4:  2 records, different frameworks, into a third framework
    Desired result:  merge with third framework used