i18n: Register Include

This addresses issue 4965 where the register.inc.php file for clients was
missing translations for the action buttons.

include/client/register.inc.php

@@ -92,8 +92,8 @@ $info = Format::htmlchars(($errors && $_POST)?$_POST:$info);
 </table>
 <hr>
 <p style="text-align: center;">
-    <input type="submit" value="Register"/>
-    <input type="button" value="Cancel" onclick="javascript:
+    <input type="submit" value="<?php echo __('Register'); ?>"/>
+    <input type="button" value="<?php echo __('Cancel'); ?>" onclick="javascript:
         window.location.href='index.php';"/>
 </p>
 </form>