fix compile warning about unchecked generic type
make './sbt scalding-repl/run' work

Needed to add provided libs back in and setup interpretter's
default settings correctly.
add comments to try to explain the sbt build mumbo jumbo
default to '--local' mode
un-default to '--local' mode
manually set 'usejavacp' when running from assembly, and add test for sbt run
Merge pull request #1021 from twitter/bholt/sbt-run

Run REPL from SBT