Bug 6298 : Add optional dependency on Gravatar::URL 1.03

Bug 6298 : Add optional dependency on Gravatar::URL 1.03

This CPAN module is needed for the ShowReviewerPhoto functionality.

Unfortunately the version in Squeeze (1.02) is not sufficient so it
has to be installed from CPAN:

  sudo apt-get install libnet-dns-perl libtest-warn-perl
  sudo cpan Gravatar::URL

Signed-off-by: Francois Marier <francois@debian.org>
Signed-off-by: Nicole C. Engard <nengard@bywatersolutions.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>