Revert "SPARK-1236 - Upgrade Jetty to 9.1.3.v20140225."

This reverts commit ca4bf8c572c2f70b484830f1db414b5073744ab6.

Jetty 9 requires JDK7 which is probably not a dependency we want to bump right now. Before Spark 1.0 we should consider upgrading to Jetty 8. However, in the mean time to ease some pain let's revert this. Sorry for not catching this during the initial review. cc/ @rxin