[3.1.0] multitest.php now works again for all version, however, some hacks to PHPT are required

- Bootstrap hotfix to prevent multiple loading in standalone. We need a better way of doing this!
- Make extras/ autoloader polite too
- Initialize autoloaders in common.php
- Add trailing dash to "skip" in phpt
- Upgrade SimpleTest.php not to allow directories

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@1554 48356398-32a2-884e-a903-53898d9a118a

extras/HTMLPurifierExtras.autoload.php

@@ -2,6 +2,10 @@
 
 if (function_exists('spl_autoload_register')) {
   spl_autoload_register(array('HTMLPurifierExtras', 'autoload'));
+  if (function_exists('__autoload')) {
+    // be polite and ensure that userland autoload gets retained
+    spl_autoload_register('__autoload');
+  }
 } elseif (!function_exists('__autoload')) {
   function __autoload($class) {return HTMLPurifierExtras::autoload($class);}
 }