Forms implementation for %HTML.Trusted. Some backend changes:

* Added Charsets and Character attribute types
* Fix a heavily recursive form of ContentSets, this allows a content-set
  to include another content-set which includes another content-set, and
  so forth.

Signed-off-by: Edward Z. Yang <edwardzyang@thewritingpot.com>

tests/HTMLPurifier/ComplexHarness.php

@@ -80,6 +80,10 @@ class HTMLPurifier_ComplexHarness extends HTMLPurifier_Harness
         }
         $this->assertIdentical($expect, $result);
         
+        if ($expect !== $result) {
+            echo '<pre>' . htmlspecialchars($result) . '</pre>';
+        }
+        
     }
     
     /**