Added test for generation of set comprehensions where several multiple binds exists, e.g. {a+b+c+d+e+f | a,b in set {1,2}, c,d in set {2,3}, e,f in set {3,4}}
Added notion of multiple binds to the OO AST (used e.g. by set comprehensions)
Created a multiple bind visitor and added it to the OoAstInfo (the visitior 'question').
Changed set comprehensions in the OO AST to use a list of multiple set binds to provide support for the more general case where multiple set binds are specified in the set comprehension