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

- Port GTK+ clients to GTK+2. I'm not sure if I should simply replace
  one with the other, or offer them both in case users only have one
  installed (or are turned off by the size of GTK+2).

- 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.

- There may be some stuff from the netwm spec that's worth implementing.
  We already have GNOME_PANEL_DESKTOP_AREA.

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