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

mysql-test/suite/innodb_plugin/t/innodb.test

@@ -45,6 +45,15 @@ drop table if exists t1,t2,t3,t4;
 drop database if exists mysqltest;
 --enable_warnings
 
+# Bug#58912 InnoDB unnecessarily avoids update-in-place on column prefixes
+CREATE TABLE bug58912 (a BLOB, b TEXT, PRIMARY KEY(a(1))) ENGINE=InnoDB;
+INSERT INTO bug58912 VALUES(REPEAT('a',8000),REPEAT('b',8000));
+UPDATE bug58912 SET a=REPEAT('a',7999);
+# The above statements used to trigger a failure during purge when
+# Bug#55284 was fixed while Bug#58912 was not. Defer the DROP TABLE,
+# so that purge gets a chance to run (and a double free of the
+# off-page column can be detected, if one is to occur.)
+
 #
 # Small basic test with ignore
 #
@@ -2543,6 +2552,9 @@ SET GLOBAL innodb_thread_concurrency = @innodb_thread_concurrency_orig;
 
 -- enable_query_log
 
+# Clean up after the Bug#55284/Bug#58912 test case.
+DROP TABLE bug58912;
+
 #######################################################################
 #                                                                     #
 # Please, DO NOT TOUCH this file as well as the innodb.result file.   #