Fix for bug 661083: "Let developers localize add-on metadata."
https://bugzilla.mozilla.org/show_bug.cgi?id=661083

The package.json keys "title", "author", "description", and "homepage"
can be localized using the property file keys "addon_title",
"addon_author", "addon_description", and "addon_homepage".

Conflicts:
	python-lib/cuddlefish/rdf.py