Upstream: https://github.com/wikimedia/jquery.i18n
Changes:
* Support fallback loading when folder is passed as source to load
* Do not overwrite existing messages for a locale while adding messages
second time
* Fix the country code case issue
* Renamed jquery.i18n.messages.js to jquery.i18n.messagestore
* ULS: Updated Resources.php for renaming of jquery.i18n.messages file
Change-Id: I60a6e3224cb7b8ea813a8ccd7e389071b3d1244c
9c40252a72