Improved handling of machine readable MDN data

it looks like header data, but there isn't requirements regarding
newlines between entries, so need to normalize to use our existing MIME
header parsing code

imp/lib/Mime/Viewer/Mdn.php

@@ -123,7 +123,14 @@ protected function _renderInfo()
         );
 
         if ($machine) {
-            $parse = Horde_Mime_Headers::parseHeaders($machine->getContents());
+            $parse = Horde_Mime_Headers::parseHeaders(
+                /* Remove extra line endings. */
+                preg_replace(
+                    '/\n{2,}/',
+                    "\n",
+                    strtr($machine->getContents(), "\r", "\n")
+                )
+            );
 
             if (isset($parse['Final-Recipient'])) {
                 list(,$recip) = explode(