Bug 13028: Followup adding a -partial flag for partial compares

Bug 13028: Followup adding a -partial flag for partial compares

If you compare the database with a partial pref file, you may not be
interested in lots of lines saying that a pref is not in the file. You
were already aware of that ;)
If you add the -partial flag, these lines will be skipped.

Test plan:
Do as described above.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Works as described, passes tests and QA script.

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>