add Storable a => Storable (Ratio a) and Storable a => Storable (Complex a) to base

[Henning Thielemann]

On Mon, 3 Nov 2014, Carter Schonwald wrote:

> Getting those two into base for 7.10 would be quite nice. 
> I think this will mostly impact folks who maintain numerical computing libraries, such as myself, and even
> then, I think this would be a change well worth having!

Storable (Complex a) would be nice, but how can Storable (Ratio a) work 
reliably? (Storable a) means that values of type 'a' are represented by a 
fixed number of bytes. That is, for (Storable a => Ratio a) you would have 
a ratio of fixed size integers. Silent overflow in integers is already 
nasty, but in Ratios the effect of overflows is even worse.