Improve the inlining optimization to handle derived instances well

[lukaszcz]

Currently, derived instances which are recursive are inefficient, because the recursive call is done via the generic Eq.eq instead of calling the function being defined directly. Thus a recursive call is compiled to a case on the instance of Eq to fetch the function to be called. This instance should be inlined and the case eliminated. It currently isn't unless the pragma inline: case is present. This situation should be detected automatically.