- Persistent clients (ok, that's just aepanel-*) should reload their
  config files on SIGHUP.

- aepanel can't tell when an iconified window has been created. I
  don't see any easy way around this, given how SubstructureRedirect
  works. Possibly CreateNotify...?

- Obscure parts of the ICCCM that need to be implemented: WM_COLORMAPS,
  WM_TAKE_FOCUS. Shouldn't be very difficult, I just have no pressing
  need for them currently. I will bring back wm_cmap_wins[1] when I do
  this.

[1] wm_cmap_wins = XInternAtom(dpy, "WM_COLORMAP_WINDOWS", False);