work on "imposter" Tuple for ceylon/ceylon-js#147
typo
improve mock Tuple for ceylon/ceylon-js#147
several improvements to mock tuple for ceylon/ceylon-js#147
update String.slice to work with new tuple
typo
simplify String.slice
work on ceylon/ceylon-js#147 and simplify flatten
make test more general
optimize "is" for tuples in JS ceylon/ceylon-js#147