math/scilab: Update path to xml-apis-ext.jar

Also:

• Replace PORTVERSION with DISTVERSION.
• Improve search path for jar-files in general.
• Fix search jrosetta-api.jar.
• Fix search saxon-he*.jar, but this old version of scilab support saxon < 10 and textproc/saxon-he have 12.6 - math/scilab is broken and need update.