Make forkProcess work with +RTS -N
Consider this experimental for the time being. There are a lot of things that could go wrong, but I've verified that at least it works on the test cases we have. I also did some API cleanups while I was here. Previously we had: Capability * rts_eval (Capability *cap, HaskellObj p, /*out*/HaskellObj *ret); but this API is particularly error-prone: if you forget to discard the Capability * you passed in and use the return value instead, then you're in for subtle bugs with +RTS -N later on. So I changed all these functions to this form: void rts_eval (/* inout */ Capability **cap, /* in */ HaskellObj p, /* out */ HaskellObj *ret) It's much harder to use this version incorrectly, because you have to pass the Capability in by reference.