QVT — Member selection operator

With – as an OCL comment, ++ seems a very unfortunate choice of operator spelling.
It also has minimal similarity to the C/Java increment operator which is unary.
Please review. The usage seems to always be <big-clause> ++ <tiny>, so how about
just a word.

?? <big-clause> 'in' <tiny>
?? <big-clause> 'over' <tiny>
?? <big-clause> 'forall' <tiny>

Resolution: No change

Remark:
Which operator to use is a matter of taste. We checked with a few users and they preferred an operator over a keyword.