Updates to keep using the Python 2.5 runtime with App Engine 1.8.8.
Updates for Foursquare API versioning

- Log errors that are received for 200 responses
- Fix paging behavior ("end of time" hacks no longer seem necessary)
- Fix user photo and venue icon URLs (fields are now structured with a "prefix"
  and "suffix" instead of just a URL)
- Fix U.S.A. detection (country is now labelled as "United States")