Revert "use Clone only, and require it" and "Bite the bullet, require Clone."

This (mostly) reverts commit 0711754236110ac3406780012462f0474cbe6e60
and all of commit 7d31bd5626b02c7fcc920738aa17c2e010e2b00f.

Storable is fixable, see the next commit.  Clone::Fast is an unknown to
me, so I omitted reverting its removal.

The unrelated original change from

    eval "require Error"
 to eval "require Error; 1"

is also preserved.
Tell Storable to freeze and thaw CODE refs

By default it won't for security.

This reverts commit 5dd8e967998c8ccc3305c5c41c4c2d6f4b6a3395: "skip
tests if the cloning class used happens to be Storable, see bug #3447".

The failing tests from Redmine issue #3447, t/Seq/Seq.t and
t/SeqTools/SeqUtils.t, pass for me both with and without Clone
available.  I tested using -MDevel::Hide=-from:children,Clone.
Hint that installing Clone or Storable is necessary in error message

If neither Clone or Storable are available (Storable is in the Perl core
since 5.8!), provide a more useful error message when CODE refs are
encountered by our poor man's dclone.
Merge pull request #73 from tsibley/1.6/dclone-storable-fallback

Restore dclone fallback to Storable