[SPARK-1468] Modify the partition function used by partitionBy.

Make partitionBy use a tweaked version of hash as its default partition function
since the python hash function does not consistently assign the same value
to None across python processes.

Associated JIRA at https://issues.apache.org/jira/browse/SPARK-1468

Author: Erik Selin <erik.selin@jadedpixel.com>

Closes #371 from tyro89/consistent_hashing and squashes the following commits:

201c301 [Erik Selin] Make partitionBy use a tweaked version of hash as its default partition function since the python hash function does not consistently assign the same value to None across python processes.
fix java.lang.ClassCastException

get Exception when run：bin/run-example org.apache.spark.examples.sql.RDDRelation
Exception's detail is:
Exception in thread "main" java.lang.ClassCastException: java.lang.Long cannot be cast to java.lang.Integer
	at scala.runtime.BoxesRunTime.unboxToInt(BoxesRunTime.java:106)
	at org.apache.spark.sql.catalyst.expressions.GenericRow.getInt(Row.scala:145)
	at org.apache.spark.examples.sql.RDDRelation$.main(RDDRelation.scala:49)
	at org.apache.spark.examples.sql.RDDRelation.main(RDDRelation.scala)
change sql("SELECT COUNT(*) FROM records").collect().head.getInt(0) to sql("SELECT COUNT(*) FROM records").collect().head.getLong(0), then the Exception do not occur any more

Author: baishuo(白硕) <vc_java@hotmail.com>

Closes #949 from baishuo/master and squashes the following commits:

f4b319f [baishuo(白硕)] fix java.lang.ClassCastException
Synthetic GraphX Benchmark

This PR accomplishes two things:

1. It introduces a Synthetic Benchmark application that generates an arbitrarily large log-normal graph and executes either PageRank or connected components on the graph.  This can be used to profile GraphX system on arbitrary clusters without access to large graph datasets

2. This PR improves the implementation of the log-normal graph generator.

Author: Joseph E. Gonzalez <joseph.e.gonzalez@gmail.com>
Author: Ankur Dave <ankurdave@gmail.com>

Closes #720 from jegonzal/graphx_synth_benchmark and squashes the following commits:

e40812a [Ankur Dave] Exclude all of GraphX from compatibility checks vs. 1.0.0
bccccad [Ankur Dave] Fix long lines
374678a [Ankur Dave] Bugfix and style changes
1bdf39a [Joseph E. Gonzalez] updating options
d943972 [Joseph E. Gonzalez] moving the benchmark application into the examples folder.
f4f839a [Joseph E. Gonzalez] Creating a synthetic benchmark script.