Added Locale::PO dependency in Makefile.PL

In one of my setups, "install-code.pl pt-PT" complained
about a missing "Locale::PO". So, I'm adding it to
Makefile.PL. I'm using the version 0.17 as minimum
required because it's the one that's available in
Debian 5.0.2. ("lenny").

Signed-off-by: Galen Charlton <gmcharlt@gmail.com>

Makefile.PL

@@ -579,6 +579,7 @@ WriteMakefile(
                             'List::MoreUtils'                  => 0.21,
                             'Locale::Currency::Format'         => 1.28,
                             'Locale::Language'                 => 2.07,
+                            'Locale::PO'                       => 0.17,
                             'MARC::Charset'                    => 0.98,
                             'MARC::Crosswalk::DublinCore'      => 0.02,
                             'MARC::File::XML'                  => 0.88,