Create executor and planner-backend support for decoupled heap and index

scans, using in-memory tuple ID bitmaps as the intermediary.  The planner
frontend (path creation and cost estimation) is not there yet, so none
of this code can be executed.  I have tested it using some hacked planner
code that is far too ugly to see the light of day, however.  Committing
now so that the bulk of the infrastructure changes go in before the tree
drifts under me.

src/include/executor/nodeBitmapHeapscan.h

@@ -0,0 +1,25 @@
+/*-------------------------------------------------------------------------
+ *
+ * nodeBitmapHeapscan.h
+ *
+ *
+ *
+ * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * $PostgreSQL: pgsql/src/include/executor/nodeBitmapHeapscan.h,v 1.1 2005/04/19 22:35:17 tgl Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef NODEBITMAPHEAPSCAN_H
+#define NODEBITMAPHEAPSCAN_H
+
+#include "nodes/execnodes.h"
+
+extern int	ExecCountSlotsBitmapHeapScan(BitmapHeapScan *node);
+extern BitmapHeapScanState *ExecInitBitmapHeapScan(BitmapHeapScan *node, EState *estate);
+extern TupleTableSlot *ExecBitmapHeapScan(BitmapHeapScanState *node);
+extern void ExecEndBitmapHeapScan(BitmapHeapScanState *node);
+extern void ExecBitmapHeapReScan(BitmapHeapScanState *node, ExprContext *exprCtxt);
+
+#endif   /* NODEBITMAPHEAPSCAN_H */