Update from version 1.313 to 1.315.

Pkgsrc changes:
o Fix MASTER_SITES
o Fix up DEPENDS acocrding to updated dependencies
o Change HOMEPAGE to use searc.cpan.org and standardized URL

Upstream changes:

1.315    2008-07-08
          http://rt.cpan.org/Public/Bug/Display.html?id=20536
          improve docs, improve handling of nested multipart
          thanks to DROLSKY and to the guys at Best Practical

1.314    2007-10-02
          bug fix: bump up prereq on Email::MIME::Modifier
          (fixes a scalar deref issue, reported by JESSE)

(he)