(Ported from https://github.com/apache/incubator-spark/pull/650 )

This adds one more change though, to fix the scala version warning introduced by json4s recently.

Author: Sean Owen <sowen@cloudera.com>

Closes #32 from srowen/SPARK-1084.2 and squashes the following commits:

9240abd [Sean Owen] Avoid scala version conflict in scalap induced by json4s dependency
1561cec [Sean Owen] Remove "exclude *" dependencies that are causing Maven warnings, and that are apparently unneeded anyway