[SPARK-2135][SQL] Use planner for in-memory scans

Author: Michael Armbrust <michael@databricks.com>

Closes #1072 from marmbrus/cachedStars and squashes the following commits:

8757c8e [Michael Armbrust] Use planner for in-memory scans.

Conflicts:
	sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala
Offheap setup

Conflicts:
	sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala