Initial import of p5-libxml (aka libxml-perl).

Initial import of p5-libxml (aka libxml-perl).

p5-libxml is a collection of smaller Perl modules, scripts, and
documents for working with XML in Perl.  p5-libxml software works in
combination with XML::Parser, PerlSAX, XML::DOM, XML::Grove and
others.

Provided by Nathan Ahlstrom <nrahlstr@winternet.com> in PR #12641.

Note that the distfile is called "libxml-perl", Nathan submitted the
package as "p5-libxml-perl", and I decided to import it as "p5-libxml"
to remove some redundancy.  I hope this doesn't cause confusion.