match region_id along with name and country_id when doing existing city lookups

I just tried an import with the cities1000.zip database with a filter for only US cities.

After the import, I noticed Philadelphia, PA was not in the database, but rather just Philadelphia, MS.  At present, there are 3 cities with populations > 1000 with the name Philadelphia in the US, but the import was picking up only Philadelphia, MS, the first one in the cities1000 file

I took a shot at fixing this by including region_id in the kwargs for city lookup.  I'm not sure why the region was not included before, so I don't know if this change may have any affect on any other datasets, particularly for those cities not in the U.S.