1.0.37.38: micro-optimizations of CONCATENATE bits

1.0.37.38: micro-optimizations of CONCATENATE bits

- Don't insert array bounds checks when inlining CONCATENATE.  This
  particularly helps when smushing together constant strings.

- Don't insert array bounds checks in the out-of-line CONCATENATE functions.

- While we're here, tweak the REPLACE transforms to avoid bounds checking
  under appropriate policy.