Null-merge the following changeset from mysql-trunk-merge:

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revision-id: joro@sun.com-20100118155046-v6hvlyfmitcyep8p
committer: Georgi Kodinov <joro@sun.com>
branch nick: B45989-5.1-bugteam
timestamp: Mon 2010-01-18 17:50:46 +0200
message:
  Bug #45989 take 2 : memory leak after explain encounters an
  error in the query.
  
  Fixes a leak after materializing a GROUP BY subquery to a 
  temp table when the subquery has a blob column in the SELECT
  list.
  Fixed by correctly destructing temporary buffers after doing
  the conversion.
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