Fixed a bug that allowed use of database names containing a . character. This fixes a serious security issue when mysqld is run as root.
Fixed bug when thread creation failed (could happen when doing a lot of connections in a short time).
Fixed some problems with FLUSH TABLES and TEMPORARY tables. (Problem with freeing the key cache and error Can't reopen table....)
Fixed a problem in InnoDB with other character sets than latin1 and another problem when using many columns.
Fixed bug that caused a core dump when using a very complex query involving DISTINCT and summary functions.
Added SET TRANSACTION ISOLATION LEVEL ...
Added SELECT ... FOR UPDATE.
Fixed bug where the number of affected rows was not returned when MySQL was compiled without transaction support.
Fixed a bug in UPDATE where keys weren't always used to find the rows to be updated.
Fixed a bug in CONCAT_WS() where it returned incorrect results.
Changed CREATE ... SELECT and INSERT ... SELECT to not allow concurrent inserts as this could make the binary log hard to repeat. (Concurrent inserts are enabled if you are not using the binary or update log.)
Changed some macros to be able to use fast mutex with glibc 2.2.