fixed two tests in XMLParserTests; updated README.md

Instead of
      self assert: error = 'this collection is empty'.

it is necessary to do
      self assert: error messageText = 'this collection is empty'.

The README.md now references the more comprehensive ports list at
https://github.com/jvuletich/Cuis/blob/master/ListOfCuisPackages.md
and only lists the ones which are actually in this repository.