added tests for new set operations and empty list cases
added tests for new set operations and empty list cases

svn path=/trunk/StrategoXT/; revision=1569

lichtemo/strategoxt,lichtemo/strategoxt,lichtemo/strategoxt,lichtemo/strategoxt,metaborg/strategoxt,metaborg/strategoxt,Apanatshka/strategoxt,metaborg/strategoxt,Apanatshka/strategoxt,lichtemo/strategoxt,metaborg/strategoxt,Apanatshka/strategoxt,Apanatshka/strategoxt,Apanatshka/strategoxt,metaborg/strategoxt