Clean up messy clause-selectivity code in clausesel.c; repair bug

identified by Hiroshi (incorrect cost attributed to OR clauses
after multiple passes through set_rest_selec()).  I think the code
was trying to allow selectivities of OR subclauses to be passed in
from outside, but noplace was actually passing any useful data, and
set_rest_selec() was passing wrong data.

Restructure representation of "indexqual" in IndexPath nodes so that
it is the same as for indxqual in completed IndexScan nodes: namely,
a toplevel list with an entry for each pass of the index scan, having
sublists that are implicitly-ANDed index qual conditions for that pass.
You don't want to know what the old representation was :-(

Improve documentation of OR-clause indexscan functions.

Remove useless 'notclause' field from RestrictInfo nodes.  (This might
force an initdb for anyone who has stored rules containing RestrictInfos,
but I do not think that RestrictInfo ever appears in completed plans.)

src/backend/nodes/outfuncs.c

@@ -5,7 +5,7 @@
  *
  * Copyright (c) 1994, Regents of the University of California
  *
- *	$Id: outfuncs.c,v 1.90 1999/07/18 19:02:49 tgl Exp $
+ *	$Id: outfuncs.c,v 1.91 1999/07/24 23:21:07 tgl Exp $
  *
  * NOTES
  *	  Every (plan) node in POSTGRES has an associated "out" routine which
@@ -1110,9 +1110,8 @@ _outRestrictInfo(StringInfo str, RestrictInfo *node)
 	_outNode(str, node->clause);
 
 	appendStringInfo(str,
-					 " :selectivity %f :notclause %s :indexids ",
-					 node->selectivity,
-					 node->notclause ? "true" : "false");
+					 " :selectivity %f :indexids ",
+					 node->selectivity);
 	_outNode(str, node->indexids);
 
 	appendStringInfo(str, " :mergejoinorder ");