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/optimizer/util/pathnode.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/util/pathnode.c,v 1.46 1999/07/16 04:59:25 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/util/pathnode.c,v 1.47 1999/07/24 23:21:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -426,7 +426,8 @@ create_index_path(Query *root,
 		/* each clause gets an equal selectivity */
 		clausesel = pow(selec, 1.0 / (double) length(restriction_clauses));
 
-		pathnode->indexqual = restriction_clauses;
+		pathnode->indexqual = lcons(get_actual_clauses(restriction_clauses),
+									NIL);
 		pathnode->path.path_cost = cost_index(lfirsti(index->relids),
 											  (int) npages,
 											  selec,