IMPALA-1412: Create view as select produces incorrect results

This commit fixes the issue where querying a view produces incorrect
results if the view definition statement references the same column
multiple times in the select list. In that case, a predicate referencing
the same slot is generated when equivalences among view slots are
enforced, thereby causing null values to be rejected.

Change-Id: I3d13656141fb41d232ddd38562cbde277f2a1264
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5031
Reviewed-by: Dimitris Tsirogiannis <dtsirogiannis@cloudera.com>
Tested-by: jenkins