each line's object rather than a singleton object so that we can ship
these classes to worker nodes). This is pretty hairy stuff, which would
be nice to avoid in the future by integrating with the interpreter some
other way.

Conflicts:
	project/build/SparkProject.scala

As Matei described: "We're using Jetty to run an HTTP server, not to embed Spark
in a webapp"

Use explicit asInstanceOf instead of misleading unchecked pattern matching.

The repl module requires more complex work.

Upgrade some of the dependencies while at it.

Also enable -unchecked warnings in SBT build file.

Fix deprecations when compiled with Scala 2.8.1

tabulate used if indexed used by function and fill otherwise.

thus clean up the various singletons (RDDCache, MapOutputTracker, etc).
This isn't perfect yet (ideally we shouldn't use singleton objects at
all) but we can fix that later.