core: Make errno message a part of errno exceptions

[AndreasMadsen]

To people like me there don't use enough time with errno codes it can be difficult to remember what EBADF means. This add a text message to all errno exceptions, like bad file descriptor.

The messages are from get_uv_errno_message, to use this it was necessary to change the SetError so it set errno to a number and not get_uv_errno_string.

I'm hoping we later could abstract ErrnoException from node.cc to use Errno::ErrnoException.

It would also be nice to have binding functions return an uv_errno number instead of 1 or 0. This way we won't pollute global scope with errno.

Example of this patch:

var Pipe = process.binding('pipe_wrap').Pipe;
var errnoException = process.binding('errno').errnoException;

var stream = new Pipe(true);
    stream.close();

var buffer = new Buffer("test");
var errno = stream.write(buffer, 0, buffer.length);
if (errno !== 0) {
  throw errnoException(errno, 'write');
}

@piscisaureus told me that you did not want any errno changes now, but since I had made the patch why not allow you to reconsider.

[bnoordhuis]

It would also be nice to have binding functions return an uv_errno number instead of 1 or 0. This way we won't pollute global scope with errno. Example of this:

Agreed. We could (and probably should) copy the Linux kernel convention here: return >=0 on succes, -ERRNUM on error.

[Nodejs-Jenkins]

Can one of the admins verify this patch?

[tjfontaine]

This work has been done in libuv and in node, in various commits. libuv now directly returns the errno and we map that to a useful value and include the syscall