v2.21

        Many more improvements from Niels Thykier, great hero of the
        free people. Plus a compatibility patch from Zefram, keeper
        of Carp.

        * SPEED / INTERNAL : Through the magic of globally reuseable
          core leak trampolines, autodie is even faster when used across
          multiple pacakages.

        * SPEED / INTERNAL : Caches used for keeping track of
          fatalised subroutines are faster and leaner.

        * SPEED / INTERNAL : Core subroutine wrappers are now lazily
          compiled.

        * SPEED / INTERNAL : Using autodie while autodie is already in
          effect is now faster and more efficient.

        * INTERNAL : $" and $! are no longer arbitrarily messed with
          for no reason via autodie.  (They're still messed with when
          using Fatal.)

        * SPEED / INTERNAL : The ':all' tag hierachy is expanded
          immediately, in an efficient fashion.

        * INTERNAL : Numerous minor clean-ups. Dead variables removed.
          Typos fixed.

        * SPEED / INTERNAL : import() and _make_fatal() cache more
          aggressively, reducing CPU overhead.

        * TEST: Compatibility with Carp 1.32 (thanks to Zefram).
          RT #88076.