SPARK-1019: pyspark RDD take() throws an NPE

Author: Patrick Wendell <pwendell@gmail.com>

Closes #112 from pwendell/pyspark-take and squashes the following commits:

daae80e [Patrick Wendell] SPARK-1019: pyspark RDD take() throws an NPE
[SPARK-1237, 1238] Improve the computation of YtY for implicit ALS

Computing YtY can be implemented using BLAS's DSPR operations instead of generating y_i y_i^T and then combining them. The latter generates many k-by-k matrices. On the movielens data, this change improves the performance by 10-20%. The algorithm remains the same, verified by computing RMSE on the movielens data.

To compare the results, I also added an option to set a random seed in ALS.

JIRA:
1. https://spark-project.atlassian.net/browse/SPARK-1237
2. https://spark-project.atlassian.net/browse/SPARK-1238

Author: Xiangrui Meng <meng@databricks.com>

Closes #131 from mengxr/als and squashes the following commits:

ed00432 [Xiangrui Meng] minor changes
d984623 [Xiangrui Meng] minor changes
2fc1641 [Xiangrui Meng] remove commented code
4c7cde2 [Xiangrui Meng] allow specifying a random seed in ALS
200bef0 [Xiangrui Meng] optimize computeYtY and updateBlock
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.
[bugfix] wrong client arg, should use executor-cores

client arg is wrong, it should be executor-cores. it causes executor fail to start when executor-cores is specified

Author: Tianshuo Deng <tdeng@twitter.com>

Closes #138 from tsdeng/bugfix_wrong_client_args and squashes the following commits:

304826d [Tianshuo Deng] wrong client arg, should use executor-cores
SPARK-1162 added takeOrdered to pyspark