Bug#51851: Server with SBR locks mutex twice on

LOAD DATA into partitioned MyISAM table

Problem was that both partitioning and myisam
used the same table_share->mutex for different protections
(auto inc and repair).

Solved by adding a specific mutex for the partitioning
auto_increment.

Also adding destroying the ha_data structure in
free_table_share (which is to be propagated
into 5.5).

This is a 5.1 ONLY patch, already fixed in 5.5+.

sql/table.h

@@ -463,6 +463,7 @@ typedef struct st_table_share
 
   /** place to store storage engine specific data */
   void *ha_data;
+  void (*ha_data_destroy)(void *); /* An optional destructor for ha_data. */
 
 
   /*