use `pop-to-buffer` for *command-log* buffer, so it can be managed by other extension.

[stardiviner]

I wish *command-log* buffer can show in any position which I want. the extension https://github.com/m2ym/popwin-el can be used to manage popup buffers.
I wish command-log-mode can use popup-to-buffer by default, or provide an option like command-log-mode-use-popwin or a condition to detect popwin exist, if exist, then use pop-to-buffer, if not, use original split widnow style.