* Fri Oct 14 14:04:01 PDT 2016

* stray println

## What changes were proposed in this pull request?

This PR aims to optimize GroupExpressions by removing repeating expressions. `RemoveRepetitionFromGroupExpressions` is added.

**Before**
```scala
scala> sql("select a+1 from values 1,2 T(a) group by a+1, 1+a, A+1, 1+A").explain()
== Physical Plan ==
WholeStageCodegen
:  +- TungstenAggregate(key=[(a#0 + 1)#6,(1 + a#0)#7,(A#0 + 1)#8,(1 + A#0)#9], functions=[], output=[(a + 1)#5])
:     +- INPUT
+- Exchange hashpartitioning((a#0 + 1)#6, (1 + a#0)#7, (A#0 + 1)#8, (1 + A#0)#9, 200), None
   +- WholeStageCodegen
      :  +- TungstenAggregate(key=[(a#0 + 1) AS (a#0 + 1)#6,(1 + a#0) AS (1 + a#0)#7,(A#0 + 1) AS (A#0 + 1)#8,(1 + A#0) AS (1 + A#0)#9], functions=[], output=[(a#0 + 1)#6,(1 + a#0)#7,(A#0 + 1)#8,(1 + A#0)#9])
      :     +- INPUT
      +- LocalTableScan [a#0], [[1],[2]]
```

**After**
```scala
scala> sql("select a+1 from values 1,2 T(a) group by a+1, 1+a, A+1, 1+A").explain()
== Physical Plan ==
WholeStageCodegen
:  +- TungstenAggregate(key=[(a#0 + 1)#6], functions=[], output=[(a + 1)#5])
:     +- INPUT
+- Exchange hashpartitioning((a#0 + 1)#6, 200), None
   +- WholeStageCodegen
      :  +- TungstenAggregate(key=[(a#0 + 1) AS (a#0 + 1)#6], functions=[], output=[(a#0 + 1)#6])
      :     +- INPUT
      +- LocalTableScan [a#0], [[1],[2]]
```

## How was this patch tested?

Pass the Jenkins tests (with a new testcase)

Author: Dongjoon Hyun <[email protected]>

Closes apache#12590 from dongjoon-hyun/SPARK-14830.

(cherry picked from commit 6e63201)
Signed-off-by: Michael Armbrust <[email protected]>