* module/language/cps2/cse.scm: New file, ported from CPS.
* module/language/cps2/optimize.scm: Wire up CSE.
* module/Makefile.am: Add language/cps2/cse.scm.
* module/language/cps/compile-bytecode.scm (optimize): Disable
prune-top-level-scopes on old CPS. It seems to not work if CSE has
run beforehand.
