Add Firefox addon metadata l10n patch

According to https://bugzilla.mozilla.org/show_bug.cgi?id=661083 ,
I cannot add other languages' name and description into package.json
when I use the addon-sdk. And
https://developer.mozilla.org/en-US/docs/Mozilla/Localization/Localizing_extension_descriptions
shows that I have to add l10n description into install.rdf in the .xpi,
so I write a patch file to patch it after runing `cfx xpi'.