[SPARK-2428][SQL] Add except and intersect methods to SchemaRDD.

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #1355 from ueshin/issues/SPARK-2428 and squashes the following commits:

b6fa264 [Takuya UESHIN] Add except and intersect methods to SchemaRDD.