- Constant ropagation for float and int32/int64/nativeint arithmetic.
  Constant propagation for floats can be turned off with option
  -no-float-const-prop, for codes that change FP rounding modes at
  run-time.
- Clambda / C-- / Mach: represent float constants as FP numbers of type 
  float rather than literals of type string.
- Tested for AMD64; other archs need testing.


git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14673 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02