New IO impl and modules

[Sigbjorn Finne]

Hi,

I'd encourage people to compile and test the IO, Directory, and
CPUTime support I've just committed. The added primitives call
upon misc OS functionality, which might not be present on a
particular platform (or live in a different header file etc.) I believe
I've augmented the configure script so this won't be an issue, but
you never know about these things....

btw, if you don't want Directory and/or CPUTime support, prelude.h
contains #defines that control this. 

The IO impl is mostly Haskell98 compliant; the main bit it doesn't
implement is the H98 file locking rules.

--sigbjorn