Add engine version number as comment in XML file

[rolfkleef]

With the engine version number in the XML file, it is easier to track issues against the code.

Find a clean way to insert the version number in the IATI output comment; can be done with file:///home/rolf/dev/xml/qtspecs/specifications/xpath-functions-31/html/Overview.html#func-environment-variable but where best to set this? cannot be done in Ant...