Update matching_candidates_in_table() to treat all conditions similar

Fixed also that the 'with_found_constraint parameter' to
matching_candidates_in_table() is as documented: It is now true only
if there is a reference to a previous table in the WHERE condition for
the current examined table (as it was originally documented)

Changes in test results:
- Filtered was 25% smaller for some queries (expected).
- Some join order changed (probably because the tables had very few rows).
- Some more table scans, probably because there would be fewer returned
  rows.
- Some tests exposes a bug that if there is more filtered rows, then the
  cost for table scan will be higher. This will be fixed in a later commit.

mysql-test/main/select.result

@@ -3480,7 +3480,7 @@ EXPLAIN
 SELECT a, c, d, f FROM t1,t2 WHERE a=c AND b BETWEEN 4 AND 6 AND a > 0;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	range	PRIMARY,b	b	5	NULL	3	Using index condition; Using where
-1	SIMPLE	t2	ref	c	c	5	test.t1.a	2	
+1	SIMPLE	t2	ALL	c	NULL	NULL	NULL	18	Using where; Using join buffer (flat, BNL join)
 DROP TABLE t1, t2;
 create table t1 (
 a int unsigned    not null auto_increment primary key,