replace errno() with libuv version

[vtjnash]

• convert errno() -> uv_last_error()
• convert E_codes -> libuv E_codes
• make useful: uv_strerror() / uv_err_name()

[Keno]

This is essentially done. I'll take another pass through this soon and make sure it's used everywhere, but other than that we should be good.

[ViralBShah]

@loladiro Can you fix this today/tomorrow? If not, we should push to 0.2.

[Keno]

Yes, I'll to do it tomorrow.

[StefanKarpinski]

bump: is this done? seems like we're very close...

[StefanKarpinski]

I'm moving this to 0.2.

[JeffBezanson]

I really hope this can be cleaned up. I see we now have:

UV_error_t, UVError, _uv_lastsystemerror, _uv_lasterror, struverror, uverrorname, uv_error, errno,
strerror, system_error, SystemError

Come on, this is starting to look like a PHP API.

[Keno]

We came to the conclusion that this is pretty much solved now.