localize attrs in translateFragment too; fix lint error and make lint part of the default grunt task
inline Locale.prototype.setReady
expose readyState on mozL10n
return from ctx.ready early if the ctx is ready
guard public get* methods from running if ctx is not ready

otherwise, they end up creating new locales if called too early, and then
building it with no resources (b/c the ctx is not ready)
abstract the fallback loop into ctx.getWithFallback
don't throw when not ready
if missing, return an empty string
experimental: bring interactive back and throw when context is not ready

looking at the code in certain apps (e.g. system/js/identity.js), interactive
could lead to undesired results.  these apps check mozL10n.readyState instead
relying on mozL10n.ready().  The initialize if readyState is complete OR
interactive, which sounds wrong tbh.  Interestingly, in webl10n, interactive
is set only for a split second, and always synchronously, and they it goes
back to 'loading'.

I'm going back to throwing exceptions, too.  I can see a 'Context not ready'
error in the system app;  I'm not sure where it comes from.  It looks like
maybe some get or ready is called too early.  Despite the error, things appear
to be working correctly.