[SQL] Attribute equality comparisons should be done by exprId.

Author: Michael Armbrust <michael@databricks.com>

Closes #1414 from marmbrus/exprIdResolution and squashes the following commits:

97b47bc [Michael Armbrust] Attribute equality comparisons should be done by exprId.
[SPARK-2498] [SQL] Synchronize on a lock when using scala reflection inside data type objects.

JIRA ticket: https://issues.apache.org/jira/browse/SPARK-2498

Author: Zongheng Yang <zongheng.y@gmail.com>

Closes #1423 from concretevitamin/scala-ref-catalyst and squashes the following commits:

325a149 [Zongheng Yang] Synchronize on a lock when initializing data type objects in Catalyst.