[SPARK-2395][SQL] Optimize common LIKE patterns.

Author: Michael Armbrust <michael@databricks.com>

Closes #1325 from marmbrus/slowLike and squashes the following commits:

023c3eb [Michael Armbrust] add comment.
8b421c2 [Michael Armbrust] Handle the case where the final % is actually escaped.
d34d37e [Michael Armbrust] add periods.
3bbf35f [Michael Armbrust] Roll back changes to SparkBuild
53894b1 [Michael Armbrust] Fix grammar.
4094462 [Michael Armbrust] Fix grammar.
6d3d0a0 [Michael Armbrust] Optimize common LIKE patterns.