[SPARK-2102][SQL][CORE] Add option for kryo registration required and use a resource pool in Spark SQL for Kryo instances.

Author: Ian O Connell <ioconnell@twitter.com>

Closes #1377 from ianoc/feature/SPARK-2102 and squashes the following commits:

5498566 [Ian O Connell] Docs update suggested by Patrick
20e8555 [Ian O Connell] Slight style change
f92c294 [Ian O Connell] Add docs for new KryoSerializer option
f3735c8 [Ian O Connell] Add using a kryo resource pool for the SqlSerializer
4e5c342 [Ian O Connell] Register the SparkConf for kryo, it gets swept into serialization
665805a [Ian O Connell] Add a spark.kryo.registrationRequired option for configuring the Kryo Serializer
[SPARK-2549] Functions defined inside of other functions trigger failures

Author: Prashant Sharma <prashant.s@imaginea.com>

Closes #1510 from ScrapCodes/SPARK-2549/fun-in-fun and squashes the following commits:

9458bc5 [Prashant Sharma] Tested by removing an inner function from excludes.
bc03b1c [Prashant Sharma] SPARK-2549 Functions defined inside of other functions trigger failures