[SQL]Add base row updating methods for JoinedRow

This will be helpful in join operators.

Author: Cheng Hao <hao.cheng@intel.com>

Closes #1187 from chenghao-intel/joinedRow and squashes the following commits:

87c19e3 [Cheng Hao] Add base row set methods for JoinedRow

(cherry picked from commit 133495d82672c3f34d40a6298cc80c31f91faf5c)
Signed-off-by: Michael Armbrust <michael@databricks.com>
[SPARK-2264][SQL] Fix failing CachedTableSuite

Author: Michael Armbrust <michael@databricks.com>

Closes #1201 from marmbrus/fixCacheTests and squashes the following commits:

9d87ed1 [Michael Armbrust] Use analyzer (which runs to fixed point) instead of manually removing analysis operators.

Conflicts:

	sql/core/src/test/scala/org/apache/spark/sql/CachedTableSuite.scala
Fix possible null pointer in acumulator toString

Author: Michael Armbrust <michael@databricks.com>

Closes #1204 from marmbrus/nullPointerToString and squashes the following commits:

35b5fce [Michael Armbrust] Fix possible null pointer in acumulator toString

(cherry picked from commit 2714968e1b40221739c5dfba7ca4c0c06953dbe2)
Signed-off-by: Reynold Xin <rxin@apache.org>