Backport into build-200911241145-5.1.40sp1

> ------------------------------------------------------------
> revno: 1810.3964.1
> revision-id: alexey.kopytov@sun.com-20091030155453-0vlfwki805h9os62
> parent: joerg@mysql.com-20091016122941-rf6z0keqvmlgjfto
> committer: Alexey Kopytov <Alexey.Kopytov@Sun.com>
> branch nick: my50-bug48131
> timestamp: Fri 2009-10-30 18:54:53 +0300
> message:
>   Bug #48131: crash group by with rollup, distinct, filesort,
>               with temporary tables
>   
>   There were two problems the test case from this bug was
>   triggering:
>   
>   1. JOIN::rollup_init() was supposed to wrap all constant Items
>   into another object for queries with the WITH ROLLUP modifier
>   to ensure they are never considered as constants and therefore
>   are written into temporary tables if the optimizer chooses to
>   employ them for DISTINCT/GROUP BY handling.
>   
>   However, JOIN::rollup_init() was called before
>   make_join_statistics(), so Items corresponding to fields in
>   const tables could not be handled as intended, which was
>   causing all kinds of problems later in the query execution. In
>   particular, create_tmp_table() assumed all constant items
>   except "hidden" ones to be removed earlier by remove_const()
>   which led to improperly initialized Field objects for the
>   temporary table being created. This is what was causing crashes
>   and valgrind errors in storage engines.
>   
>   2. Even when the above problem had been fixed, the query from
>   the test case produced incorrect results due to some
>   DISTINCT/GROUP BY optimizations being performed by the
>   optimizer that are inapplicable in the WITH ROLLUP case.
>   
>   Fixed by disabling inapplicable DISTINCT/GROUP BY optimizations
>   when the WITH ROLLUP modifier is present, and splitting the
>   const-wrapping part of JOIN::rollup_init() into a separate
>   method which is now invoked after make_join_statistics() when
>   the const tables are already known.

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