(keving)

Much simplified and beautified CPR analysis code.  (And also much
shorter, we'd better write this up before it disappears).

Added (constant) functions to the abstract domain. Note that
Fun^n Bot (n >= 1) == Bot and likewise for Top

Treats divergent computations as Bot (rather than Top as previous) so
non-divergent paths dominate which allows us to generate more accurate
CPR info (see e.g. chr).

We use the result of strictness analysis to tell us if an Id is
divergent (when applied to sufficient args), therefore we should run
after the strictness analysis pass.