Merge data loss on zero fields (batch mode)

As suspected in CRM-17597 it turns out that the merge batch function treats 0 as no data - meaning merging a deceased contact with a live contact results in a zombie rather than a merge conflict.

Due to sloppy coding the order matters - if the dead person comes first you get a merge. If the living person is the first in the pair you get a conflict.

This also applies to do_not_trade, do_not_email etc.

I have added a test to cover is_deceased. I also had to tweak the query object /api to allow you to get both deceased & live contacts - ie. is_deceased => array('IN' => array(0, 1);