Correct type of waitMode variable in ExecInsertIndexTuples().

It was a bool, even though it should be CEOUC_WAIT_MODE. That's unlikely
to have a negative effect with the current definition of bool (char),
but it's definitely wrong.

Discussion: 20150812084351.GD8470@awork2.anarazel.de
Backpatch: 9.5, where ON CONFLICT was merged

src/backend/executor/execIndexing.c

@@ -405,7 +405,7 @@ ExecInsertIndexTuples(TupleTableSlot *slot,
 		if (indexInfo->ii_ExclusionOps != NULL)
 		{
 			bool		violationOK;
-			bool		waitMode;
+			CEOUC_WAIT_MODE waitMode;
 
 			if (noDupErr)
 			{