Add a proper exit() call after the header()

Attempted to use this plugin without the exit() and WP continued to render
without the browser getting the Location() header.  This forces the
header() call to work as no additional response is returned to the browser.

revcanonical.php

@@ -47,6 +47,7 @@ function revcanonical_do_redirect()
   $id = substr($rq, 1, strlen($rq));
   if ($id != '' && $pl = revcanonical_unshorten($id)) {
 	  header('Location: '.$pl, true, 301);
+	  exit;
   }
 }