message: add two more UX improvement items
diff: @@ -23,8 +23,16 @@ Making counterexamples easier to read
  - we'd like a reducer for IR, perhaps a C-Reduce hack if bugpoint
  isn't good enough
  +- make CEXs relating to function call side effects easier to
  + understand, currently they show up as memory state mismatches:
  + http://volta.cs.utah.edu:8080/z/khXHQM
  +
  Usability improvements not specifically related to counterexamples
  ------------------------------------------------------------------
  - (optionally) make a note in the output when an optimization is
  correct, but would not be correct under a different datalayout
  +
  +- consider adding flags similar to --disable-undef-inputs, but for
  + float values. perhaps: `--disable-nan-inputs`, `--disable-inf-inputs`,
  + `--disable-negative-zero-inputs`
  