IMPALA-822,IMP-1271: Binding predicates on an aggregation now properly trigger slot materialization.

The bug was that the number of materialized agg-tuple slots did not correspond to the number
of materialized agg functions, due to binding predicates against an AggNode causing slot
materialization after SelectStmt.materializeRequiredSlots().
This patch fixes the issue by taking binding predicates (bound to a slot in an agg tuple)
into consideration in SelectStmt.materializeRequiredSlots().
I added a new sanity check in AggregationNode.toThrift() surfaced another issue with slot
materialization that is also fixed in this patch. The ordering exprs must be marked before
the agg exprs in SelectStmt.materializeRequiredSlots() because the odering exprs may contain
agg exprs that are only referenced inside the ORDER BY clause.

Change-Id: I1bdc0466f583907bed625ce6608938e59faee83f
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1639
Reviewed-by: Marcel Kornacker <marcel@cloudera.com>
Tested-by: jenkins