transfers.txt is not handled currently

[ninowalker]

This is what is adopted: http://code.google.com/transit/spec/transit_feed_specification.html#transfers_txt___Field_Definitions

This is what is currently implemented (for a connections.txt file): http://github.com/bmander/graphserver/blob/master/pygs/graphserver/compiler/gdb_import_gtfs.py#L155 http://github.com/bmander/graphserver/blob/master/pygs/graphserver/ext/gtfs/gtfsdb.py#L196

This is a minor change.