Clean up BeginCommand and related routines. BeginCommand and EndCommand

are now both invoked once per received SQL command (raw parsetree) from
pg_exec_query_string.  BeginCommand is actually just an empty routine
at the moment --- all its former operations have been pushed into tuple
receiver setup routines in printtup.c.  This makes for a clean distinction
between BeginCommand/EndCommand (once per command) and the tuple receiver
setup/teardown routines (once per ExecutorRun call), whereas the old code
was quite ad hoc.  Along the way, clean up the calling conventions for
ExecutorRun a little bit.

src/include/executor/execdesc.h

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: execdesc.h,v 1.17 2001/11/05 17:46:33 momjian Exp $
+ * $Id: execdesc.h,v 1.18 2002/02/27 19:35:54 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -19,6 +19,7 @@
 #include "nodes/plannodes.h"
 #include "tcop/dest.h"
 
+
 /* ----------------
  *		query descriptor:
  *	a QueryDesc encapsulates everything that the executor
@@ -31,10 +32,14 @@ typedef struct QueryDesc
 	Query	   *parsetree;
 	Plan	   *plantree;
 	CommandDest dest;			/* the destination output of the execution */
+	const char *portalName;		/* name of portal, or NULL */
+
+	TupleDesc	tupDesc;		/* set by ExecutorStart */
 } QueryDesc;
 
 /* in pquery.c */
 extern QueryDesc *CreateQueryDesc(Query *parsetree, Plan *plantree,
-				CommandDest dest);
+								  CommandDest dest, const char *portalName);
+
 
 #endif   /* EXECDESC_H  */