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/mysql-test-run.pl

@@ -1592,6 +1592,8 @@ sub collect_mysqld_features {
   my $cmd= join(" ", $exe_mysqld, @$args);
   my $list= `$cmd`;
 
+  print "cmd: $cmd\n";
+
   foreach my $line (split('\n', $list))
   {
     # First look for version