[PATCH] threads::shared 1.21

The attached patch is for threads::shared 1.21.  The main
change is the addition of a shared_clone() function that
creates a shared deep copy of non-shared data:

  my $cpy = shared_clone({'foo' => [qw/foo bar baz/]});

A new test files (clone.t) is added to the MANIFEST.

• [PATCH] threads::shared 1.21 by Jerry D. Hedden
• [PATCH - revised] threads::shared 1.21 by Jerry D. Hedden
• Re: [PATCH - revised] threads::shared 1.21 by Steve Peters