Merge with MySQL 5.1.55

- Fixed some issues with partitions and connection_string, which also fixed lp:716890 "Pre- and post-recovery crash in Aria"
- Fixed wrong assert in Aria

Now need to merge with latest xtradb before pushing 

sql/ha_partition.cc:
  Ensure that m_ordered_rec_buffer is not freed before close.
sql/mysqld.cc:
  Changed to use opt_stack_trace instead of opt_pstack.
  Removed references to pstack
sql/partition_element.h:
  Ensure that connect_string is initialized
storage/maria/ma_key_recover.c:
  Fixed wrong assert

sql/sql_table.cc

@@ -6866,7 +6866,6 @@ view_err:
 			  table->alias);
     }
 
-    VOID(pthread_mutex_lock(&LOCK_open));
     /*
       Unlike to the above case close_cached_table() below will remove ALL
       instances of TABLE from table cache (it will also remove table lock
@@ -6884,15 +6883,10 @@ view_err:
         Workaround InnoDB ending the transaction when the table instance
         is unlocked/closed (close_cached_table below), otherwise the trx
         state will differ between the server and storage engine layers.
-
-        We have to unlock LOCK_open here as otherwise we can get deadlock
-        in wait_if_global_readlock().  This is still safe as we have a
-        name lock on the table object.
       */
-      VOID(pthread_mutex_unlock(&LOCK_open));
       ha_autocommit_or_rollback(thd, 0);
-      VOID(pthread_mutex_lock(&LOCK_open));
 
+      VOID(pthread_mutex_lock(&LOCK_open));
       /*
         Then do a 'simple' rename of the table. First we need to close all
         instances of 'source' table.
@@ -6925,6 +6919,8 @@ view_err:
         }
       }
     }
+    else
+      VOID(pthread_mutex_lock(&LOCK_open));
 
     if (error == HA_ERR_WRONG_COMMAND)
     {