dedupe rules should restrict by contact type early in the process

we currently don't filter by contact_type when a dedupe rule is run until late in the process. but dedupe rules are contact_type-specific, so we can filter early in order to pair down the data set. this is particularly important when deduping orgs where the org name is a rule field (quite common). since individuals with a current employer have the org name cached in their record, the current code looks for dupes across both indivs and orgs unnecessarily.

see attached patch