[SPARK-7724] [SQL] Support Intersect/Except in Catalyst DSL.

Author: Santiago M. Mola <santi@mola.io>

Closes #6327 from smola/feature/catalyst-dsl-set-ops and squashes the following commits:

11db778 [Santiago M. Mola] [SPARK-7724] [SQL] Support Intersect/Except in Catalyst DSL.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/dsl/package.scala

@@ -276,6 +276,10 @@ package object dsl {
 
     def unionAll(otherPlan: LogicalPlan): LogicalPlan = Union(logicalPlan, otherPlan)
 
+    def except(otherPlan: LogicalPlan): LogicalPlan = Except(logicalPlan, otherPlan)
+
+    def intersect(otherPlan: LogicalPlan): LogicalPlan = Intersect(logicalPlan, otherPlan)
+
     def sfilter[T1](arg1: Symbol)(udf: (T1) => Boolean): LogicalPlan =
       Filter(ScalaUdf(udf, BooleanType, Seq(UnresolvedAttribute(arg1.name))), logicalPlan)