[dev] [dwm] Popup bar patch

I have written a little patch which will pop up the bar (if it is
hidden) whilst a key is held down, over the top of all the windows. It
allows you to "peek" at the window title/status/tags without actually
unhiding the bar.

I have it set to pop up when Super_L or Super_R is held down, as these
are the modifier keys which all my key bindings use. I didn't bother
adding a config.h option for which key(s) pop up the bar, but it could
easily be done.

The patch is against hg tip (as of a few days ago anyway).

-- 
Thomas Spurden