Fixed bug #52636.

Applied the fix for bug #47217 from the mysql-6.0 codebase.
The patch adds not null predicates generated for the left parts
of the equality predicates used for ref accesses. This is done
for such predicates both in where conditions and on conditions.
For the where conditions the not null predicates were generated
but in 5.0/5.1 they actually never were used due to some lame
merge from 4.1 to 5.0. The fix for bug #47217 made these 
predicates to be used in the condition pushed to the tables.
Yet only this patch generates not null predicates for equality
predicated from on conditions of outer joins.
This patch introduces a performance regression that can be
observed on a test case from null_key.test. The regression
will disappear after the fix for bug #57024 from mariadb-5.1
is pulled into mariadb-5.3.
The patch contains many changes in the outputs of the EXPLAIN 
commands since generated not null predicates are considered as
parts of the conditions pushed to join tables and may add
'Usingwhere' in some rows of EXPLAINs where there used
to be no such comments.

1 files changed, 1 insertions, 1 deletions

diff --git a/mysql-test/r/order_by.result b/mysql-test/r/order_by.result
index dcd40f66365..fc1cd57dd28 100644
--- a/mysql-test/r/order_by.result
+++ b/mysql-test/r/order_by.result
@@ -1489,7 +1489,7 @@ SELECT d FROM t1, t2
 WHERE t2.b=14 AND t2.a=t1.a AND 5.1<t2.c AND t1.b='DE'
 ORDER BY t2.c LIMIT 1;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
-1	SIMPLE	t1	ref	a,b	b	4	const	4	Using index condition; Using temporary; Using filesort
+1	SIMPLE	t1	ref	a,b	b	4	const	4	Using index condition; Using where; Using temporary; Using filesort
 1	SIMPLE	t2	ref	a,b,c	a	40	test.t1.a,const	11	Using index condition
 SELECT d FROM t1, t2
 WHERE t2.b=14 AND t2.a=t1.a AND 5.1<t2.c AND t1.b='DE'