Optionally include Hive as a dependency of the REPL.

Due to the way spark-shell launches from an assembly jar, I don't think this change will affect anyone who isn't trying to launch the shell directly from sbt.  That said, it is kinda nice to be able to launch all things directly from SBT when developing.

Author: Michael Armbrust <michael@databricks.com>

Closes #801 from marmbrus/hiveRepl and squashes the following commits:

9570571 [Michael Armbrust] Optionally include Hive as a dependency of the REPL.

(cherry picked from commit 7463cd248f81975bce9ff864002932864bd5b649)
Signed-off-by: Aaron Davidson <aaron@databricks.com>