next libuv upgrade: status mayhem

This is the companion PR to https://github.com/joyent/libuv/pull/1190

Once that lands and a libuv release is made I'll do the libuv integration into node as primised, adapting it to changes in `uv_cwd` and the status parameter of the uv callbacks.

This PR tests exactly that. I upgraded current libuv master, that's why it's labeled "WIP".

All node tests pass for me, which gives me a certain degree of confidence ;-)

I have one doubt though: I see that timer_wrap.Timer calls its callback with the status argument, which has always been zero. Since we no longer have it, I removed it and nothing blew up. I guess it was never used or something, please have a close look at that.

/cc @tjfontaine @indutny