Remember ConnectionManagerId used to initiate SendingConnections.

This prevents ConnectionManager from getting confused if a machine
has multiple host names and the one getHostName() finds happens
not to be the one that was passed from, e.g., the BlockManagerMaster.
Use Mesos ExecutorIDs to hold SlaveIDs. Then we can safely use
the Mesos ExecutorID as a Spark ExecutorID.
Remove remants of attempt to use slaveId-executorId in MesosExecutorBackend
Include message and exitStatus if availalbe.
Merge pull request #429 from stephenh/includemessage

Include message and exitStatus if availalbe.
Merge pull request #428 from woggling/mesos-exec-id

Make ExecutorIDs include SlaveIDs when running Mesos
Merge pull request #426 from woggling/conn-manager-ips

Remember ConnectionManagerId used to initiate SendingConnections
Inclue packaging and launching pyspark in guide.

It's nicer if all the commands you need are made explicit.
Make module help available in python shell.

Also, adds a line in doc explaining how to use.
Merge pull request #430 from pwendell/pyspark-guide

Minor improvements to PySpark docs