Added a case for bug #4976 when one of the inner tables is empty.
select.result, join.result:
Reversed the previous change of the erronious fix for bug #4976.
sql_select.cc:
The previous fix for bug 4976 was reversed as it
erroniously converted an outer join into an innner join
when on_expression does not refer to outer tables.
This is not valid if inner tables return an empty set.
Setting dependency on outer tables was added for the above cases.
To fix the crash in the test case of bug #4976
a guard was added that blocks running the crashing code for
nested outer joins.
Fixed bug #4976.
join_nested.result, join_nested.test:
Added a test case for bug #4976.
sql_select.cc:
Applied conversion from an outer join to an inner join
when the on expression does not depend on the outer table.
It fixed bug #4976.
Added a test case for bug #4922.
sql_select.cc:
Blocked an optimization performed by join_read_const_table when
applied to an inner table of a nested outer join.
It was done to fix bug #4922.
sql_yacc.yy:
Fixed a typo bug in the rule for join_table.
