Fix fallback path through multipart locales

Add locale lookup with decreasing part(s) of given locale, till the
locale is only two chars long (if the id isn't in this minimal locale
version, we take the fallback or nothing) or we've found a locale
where the message exists
Add emergency brake into while loop - just for don't breaking the whole
application, if something goes wrong :)
Run index-with-es5-shim.html in travis-ci