remerge 5.1 => 5.5

sql/filesort.cc

-/* Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved.
+/*
+   Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -199,7 +200,8 @@ ha_rows filesort(THD *thd, TABLE *table, SORT_FIELD *sortorder, uint s_length,
 
   {
     const ulong min_sort_memory=
-      max(MIN_SORT_MEMORY, param.sort_length * MERGEBUFF2);
+      max(MIN_SORT_MEMORY,
+          ALIGN_SIZE(MERGEBUFF2 * (param.rec_length + sizeof(uchar*))));
     while (memory_available >= min_sort_memory)
     {
       ulong keys= memory_available / (param.rec_length + sizeof(char*));