mem::copy() segfault

[drbeefsupreme]

cargo run ./test_data/shax.jam
Segmentation fault (core dumped)

This is a regression caused by #60 . I am still working out the parameters under which it happens, but I at least have an example: a jamfile of [[shax 0x1] 9 2 10 [6 0 3] 0 2], produced on a ship that has all of the math %sham jets implemented in hoon.hoon. So far, the layer 1 and 2 Hoon standard library calls that I've tried have worked fine, but I've only tried a handful. +shax is in layer 3.

Ares writes the jammed input to NockStack fine, but falls over when it gets to cue. I tried pumping up the amount of memory Ares up til the point that the machine could not allocate it to see if it was just using an absurd amount of memory, but this didn't result in a success.

This jamfile runs fine on Ares pre split-stack, so it is not caused by the sham jets.

https://github.com/urbit/ares/blob/jon/cue-fix/rust/ares/test_data/shax.jam

[drbeefsupreme]

Ok, looks like cue finishes fine. It's actually a problem with mem::copy(), called during preserve() as the last step of running cue().