Added two phases to the behavior installation process. Now we arrange "wires," then construct sigs (history buffers), then set up handlers on those sigs. The benefit is we now optimize long chains of behId() into a single history buffer at run time. On my machine, this makes canvas-fancy.html take 40% CPU instead of 50%, and it makes platformer.html run smoothly at 50% rather than sputtering and choking at 50%. (My system has a dual-core CPU, so this is more like 100% of a core.)