Release version needs to include XML::Parser, not there in GS 2.81

[ak19]

By accident I discovered that a Perl package is missing from the recent Greenstone 2.81 release. XML::Parser (and the Expat that it includes) were not installed on my machine that's been newly changed over to CentOS. However, the 2.81 binary's GLI requires this package to parse all the XML. This means we need to include it in the release kit since other people could encounter the same problem.