Use a custom comparator for ID numbers and DOBs

[mbauman]

In dedupe's logs, it reports:

INFO:dedupe.index:Removing stop word 47
INFO:dedupe.index:Removing stop word 9-
INFO:dedupe.index:Removing stop word 25

We're using String comparisons for both SSN and DOB — it shouldn't be removing any aspect of either as a stop word.