New approach to fixed points.

This *seems* correct, but I haven't actually tried it yet since I don't
have an assembler working. I'd really like to avoid writing a combinator
"by hand" in either bytecode or assembly, as it seems quite
complicated. I think I can avoid the complexity by relying on the
implicit dataflow possible in JavaScript (implicit
copying/swapping/quotation due to having names and not a stack).