Workaround for bug #27

Awesome wm still honors aspect ratio window hints when a request for
fullscreen is made, resulting in a weird window state. This bug can be
circumvented by updating the hints before requesting fullscreen.
Spectre backend: Work with remote/memory files
Proper fullscreen for window-managers not supporting _NET_WM_ACTION_FULLSCREEN
Code cleanup
Unload images before exiting

This is required for the spectre backend, which might create temporary
files that need deletion.