Add support for unrecognized elements in MakeWellFormed.

The MakeWellFormed strategy uses metadata from HTMLDefinition in order to
determine whether or not tokens need to be converted or tags need to be
auto-closed. While this functionality is good to have, it is by no means
essential, and MakeWellFormed should not error when this information is not
available.

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

tests/HTMLPurifier/Strategy/MakeWellFormedTest.php

@@ -86,5 +86,12 @@ class HTMLPurifier_Strategy_MakeWellFormedTest extends HTMLPurifier_StrategyHarn
         );
     }
     
+    function testUnrecognized() {
+        $this->assertResult(
+            '<asdf><foobar /><biddles>foo</asdf>',
+            '<asdf><foobar /><biddles>foo</biddles></asdf>'
+        );
+    }
+    
 }