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

mysql-test/include/mtr_warnings.sql

@@ -193,6 +193,8 @@ INSERT INTO global_suppressions VALUES
  ("==[0-9]*== For more details"),
  /* This comes with innodb plugin tests */
  ("==[0-9]*== Warning: set address range perms: large range"),
+ /* valgrind-3.5.0 dumps this */
+ ("==[0-9]*== Command: "),
 
  /* valgrind warnings: invalid file descriptor -1 in syscall
     write()/read(). Bug #50414 */