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/ChildDef/RequiredTest.php

@@ -67,8 +67,6 @@ class HTMLPurifier_ChildDef_RequiredTest extends HTMLPurifier_ChildDefHarness
             'Out <b>Bold text</b><img />',
             'Out <b>Bold text</b>&lt;img /&gt;'
         );
-        
     }
-    
 }