It hasn't 
I intend for this to be one of the first things we work on for the upcoming release, but for now we still have to settle on a message format. Contributions are more than welcome 
That said, I'd usually advice against copying code from the repo directly, and suggest only working with published versions.
An issue to consider is that an error may happen way down the call stack, so a message saying 'integer overflow' may not be very useful when e.g. participating on a crowdsale. I don't think we'll be able to address this though with just these messages.
Our release cycle post has the information you're looking for. In the case of v2.3, it is scheduled to come out on April 20th.