New IO impl and modules

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