Updated from version 0.20nb1 to 0.21.

Pkgsrc changes:
o Adapt to .zip dist file suffix

Upsream changes:

0.21    Nov 6 2008

        - Added 'See also: Sub::Prepend'

        - Makefile.PL rewritten

        - support of 5.6+ only made explicit

        - Moved tests to t/. Silenced warnings.

        - Added pod.t

(he)