Add popwin support through around advices

Hi Pei,

This PR adds popwin support.

I needed it for my Emacs distribution because it uses heavily [guide-key](https://github.com/kai2nenobu/guide-key), by extension the fix should work for all popups. This solution has been tested in a non trivial Emacs configuration and works nicely (see [spacemacs](https://github.com/syl20bnr/spacemacs)).

I tried the hack with the hooks (https://github.com/jaypei/emacs-neotree/issues/50) but it has limitation like not being able to perform action when the popup window actually closes.

Cheers,
syl20bnr