A pre-requisite patch for the fix for Bug#52044.

This patch also fixes Bug#55452 "SET PASSWORD is
replicated twice in RBR mode".

The goal of this patch is to remove the release of 
metadata locks from close_thread_tables().
This is necessary to not mistakenly release
the locks in the course of a multi-step
operation that involves multiple close_thread_tables()
or close_tables_for_reopen().

On the same token, move statement commit outside 
close_thread_tables().

Other cleanups:
Cleanup COM_FIELD_LIST.
Don't call close_thread_tables() in COM_SHUTDOWN -- there
are no open tables there that can be closed (we leave
the locked tables mode in THD destructor, and this
close_thread_tables() won't leave it anyway).

Make open_and_lock_tables() and open_and_lock_tables_derived()
call close_thread_tables() upon failure.
Remove the calls to close_thread_tables() that are now
unnecessary.

Simplify the back off condition in Open_table_context.

Streamline metadata lock handling in LOCK TABLES 
implementation.

Add asserts to ensure correct life cycle of 
statement transaction in a session.

Remove a piece of dead code that has also become redundant
after the fix for Bug 37521.

sql/sql_partition.cc

@@ -59,7 +59,7 @@
 #include "my_md5.h"
 #include "transaction.h"
 
-#include "sql_base.h"                           // close_thread_tables
+#include "sql_base.h"                   // close_all_tables_for_name
 #include "sql_table.h"                  // build_table_filename,
                                         // build_table_shadow_filename,
                                         // table_to_filename
@@ -6758,7 +6758,6 @@ uint fast_alter_partition_table(THD *thd, TABLE *table,
                                  table_list, FALSE, NULL,
                                  written_bin_log));
 err:
-  close_thread_tables(thd);
   DBUG_RETURN(TRUE);
 }
 #endif