Make %URI.Munge respect %URI.Host (don't munge).

%URI.Munge incorrectly munged URIs that pointed to the
same host as the current website (it did, however, have
the correct behavior for when the munge URL was on the
same server).

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>

library/HTMLPurifier/URIFilter/Munge.php

@@ -23,6 +23,10 @@ class HTMLPurifier_URIFilter_Munge extends HTMLPurifier_URIFilter
         if (is_null($uri->host) || empty($scheme_obj->browsable)) {
             return true;
         }
+        // don't redirect if target host is our host
+        if ($uri->host === $config->getDefinition('URI')->host) {
+            return true;
+        }
 
         $this->makeReplace($uri, $config, $context);
         $this->replace = array_map('rawurlencode', $this->replace);