Automatically convert %2$s etc to %s etc for nonlocalized build. 

It is a little more fragile than the gettext `_()`, but the places which break it don't work correctly anyway and should be fixed. (I fixed them, but you never know when some more will crop up.)

I'd appreciate a critical look at `strip_positional_formatting()` in the new translations.cpp. I don't really like how i did it, but it seems to work, and should be relatively efficient.

Almost certainly fixes #2639.