add hadoop MapFile
make MapFileConcurrentReader that is identical to MapFile.Reader except for name (doesn't compile)
Simplified MapFileConcurrentReader.

- "Concurrent" because there's more than one lock per instance, but it's
  still kind of a lie because it's just implemented by having a bunch of
  SequenceFile.Reader's behind it.
cut down on requests to mapfiles in revgeo

Conflicts:
	server/src/main/scala/ReverseGeocoderImpl.scala