Change reg-ex's to global to pass unit tests

(Previously they were only uppercasing the first match.  I think Haxe 3's
regex engine, or neko 2s, has changed and is more correct)
Changed back to format() not formatOld()

Now format() if it doesn't match one of the shortcut strings, passes
through to FormatDate.format() - there shouldn't be any overlap in
real world usage.
Add comment about failing unit test on neko.

It turns out even this fails:

    d = new Date(2012, 3, 1, 0, 0, 0); // failing day

but seemingly only on this date.  SO weird.  Time for a bug report.
Not an issue on JS/AS3