utf8 patch for Storable

Storable (in bleedperl) looses utf8-ness, below is a patch to fix
that (that works for me and wasn't too heavily tested). It is against
bleedperl, if I haven't mentioned that, and it will break compatibility to
non utf8-perls.

Design rationale:

- utf8 data is common (to will be), so I allocated two extra types for
  them, rather than extending the existing SX_SCALAR/LSCALAR.

- an alternative solution would be to sv_utf8_upgrade before storing and
  sv_utf8_downgrade (if possible) after thaw'ing. Since this costs time
  and changes the utf8 state in ways users might not expect it, I decided
  against this solution.

Another issue: I think Storable tainting all my data is a bug:

$tainted = thaw freeze $ref; # no external data
my $x = retrieve_fd FILE; # tainted
my $x = <FILE>;           # tainted

I think in the first case the result should only be tainted when the input
string is.

-- 
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      ----==-- _                                           |
      ---==---(_)__  __ ____  __       Marc Lehmann      +--
      --==---/ / _ \/ // /\ \/ /       pcg@opengroup.org |e|
      -=====/_/_//_/\_,_/ /_/\_\       XX11-RIPE         --+
    The choice of a GNU generation                       |
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• utf8 patch for Storable by Marc Lehmann
• Re: utf8 patch for Storable by Raphael Manfredi