In Allegro 5, skip the buffer and just use transformations.
One word of caution, the ALLEGRO_FULLSCREEN driver isn't great, but i don't think it's entirely allegro's fault. I've tried (and others have tried) to make it work identically in all circumstances with all window managers, but it seems it is impossible.
In particular, any WM based on Compiz is just going to be broken, and not work right in general. I think metacity had issues when I last checked, but I can't remember for sure.
These days with everyone using LCDs, you really don't have more than one available resolution anyhow, so you're better off with ALLEGRO_FULLSCREEN_WINDOW and a transform.