Merge with MySQL 5.1.47

Fixed some bugs introduced in 5.1.47
Disabled some tests until we have merged with latest Xtradb

configure.in:
  Added testing if valgrind/memcheck.h exists
storage/pbxt/src/ha_pbxt.cc:
  LOCK_plugin is not anymore locked in init

sql/sql_class.h

@@ -1277,7 +1277,11 @@ struct Ha_data
     @sa trans_register_ha()
   */
   Ha_trx_info ha_info[2];
-
+  /**
+    NULL: engine is not bound to this thread
+    non-NULL: engine is bound to this thread, engine shutdown forbidden
+  */
+  plugin_ref lock;
   Ha_data() :ha_ptr(NULL) {}
 };