Initial implementation of URISchemeRegistry (fixed overload bug in process). Also, add extra notes to some of the unit tests.

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@210 48356398-32a2-884e-a903-53898d9a118a

library/HTMLPurifier/ConfigDef.php

@@ -29,6 +29,7 @@ class HTMLPurifier_ConfigDef {
             return;
         }
         if (isset($def->info[$namespace][$name])) {
+            // this behavior is at risk of change
             trigger_error('Cannot redefine directive', E_USER_ERROR);
             return;
         }