SPARK-1183. Don't use "worker" to mean executor

Author: Sandy Ryza <sandy@cloudera.com>

Closes #120 from sryza/sandy-spark-1183 and squashes the following commits:

5066a4a [Sandy Ryza] Remove "worker" in a couple comments
0bd1e46 [Sandy Ryza] Remove --am-class from usage
bfc8fe0 [Sandy Ryza] Remove am-class from doc and fix yarn-alpha
607539f [Sandy Ryza] Address review comments
74d087a [Sandy Ryza] SPARK-1183. Don't use "worker" to mean executor
SPARK-1236 - Upgrade Jetty to 9.1.3.v20140225.

Author: Reynold Xin <rxin@apache.org>

Closes #113 from rxin/jetty9 and squashes the following commits:

867a2ce [Reynold Xin] Updated Jetty version to 9.1.3.v20140225 in Maven build file.
d7c97ca [Reynold Xin] Return the correctly bound port.
d14706f [Reynold Xin] Upgrade Jetty to 9.1.3.v20140225.