Fix #29 add jobid checks

[Shougo]

@dylan-chong Please test it.

[Shougo]

@roxma Can you review/merge it?

Note: I have removed tabs.

[roxma]

It looks like the errors in #29 are triggered when exit_cb is called before err_cb or out_cb.

"exit_cb": handler	Callback for when the job ends.  The arguments are the
                        ...
                        ...
			Note that data can be buffered, callbacks may still be
			called after the process ends.

vim-hug-neovim-rpc cleanup the job entry when exit_cb is called. It doesn't look like a good place to do the cleanup.

I'm wondering, is it better to cleanup the data in close_cb?

[roxma]

If this PR is merged, we might lose data when exit_cb is called before data callbacks.

[dylan-chong]

After some research Macvim has some annoying problems being compiled with python for some reason.
In normal Vim, I don't get any problems on the current master or this branch.

Sorry if trying to fix this wasted some of your time

[Shougo]

Hm. It is related error?

Shougo/deoplete.nvim#782

[Shougo]

Closed. Because #31 is better.