Pass around the module instead of its dict (getting the latter is fast
if needed), mark function raising with negative results, check all errors,
consistent names...

We are going to die anyway, but let's do it in style.

Just use psyco_errors_init() for complete errors initialization

I guess it was unused as it only contained two init functions. The
Capsule should do things better now I guess.

The function steals a ref. The module is never destroyed so things work
fine but the refcount is wrong.