Make XML plist serializer dates work with Apple plist parser.

Apple is apparently picky about the <date> explicitly stating that it is Zulu time
and having the Z at the end.  Apparently in most versions of Qt, Qt::ISODate doesn't
include it, and it may be added in 4.8... the only way to avoid the versioning
mess is to just explicitly specify the date format in the serializer.

mythtv/libs/libmythupnp/serializers/xmlplistSerializer.cpp

@@ -92,7 +92,7 @@ void XmlPListSerializer::RenderValue(const QString &sName,
             if (needKey)
                 m_pXmlWriter->writeTextElement("key", sName);
             m_pXmlWriter->writeTextElement("date", vValue.toDateTime()
-                                           .toUTC().toString(Qt::ISODate));
+                                           .toUTC().toString("yyyy-MM-ddThh:mm:ssZ"));
             break;
         }