Fix COPY's handling of transition tables with indexes.

Commit c46c0e5202 failed to pass the
TransitionCaptureState object to ExecARInsertTriggers() in the case
where it's using heap_multi_insert and there are indexes.  Repair.

Thomas Munro, from a report by David Fetter
Discussion: https://postgr.es/m/20170708084213.GA14720%40fetter.org

src/backend/commands/copy.c

@@ -2915,7 +2915,7 @@ CopyFromInsertBatch(CopyState cstate, EState *estate, CommandId mycid,
 									  estate, false, NULL, NIL);
 			ExecARInsertTriggers(estate, resultRelInfo,
 								 bufferedTuples[i],
-								 recheckIndexes, NULL);
+								 recheckIndexes, cstate->transition_capture);
 			list_free(recheckIndexes);
 		}
 	}