Change slyEvaluateOnlyWhen to evaluate newly created children

Fix bug that was causing ngInclude to not work with sly-evaluate-only-when.

It uncovered a flaw that new elements/watchers that were added after
the sly-evaluate-only-when function had returned true (in a different
digest cycle) were never evaluated.  I'd argue that this behavior
was never really documented, so we have changed it so that the
newly added children's watchers are evaluated in a digest cycle.
This seems like a reasonable change and allows for things like
ngInclude to work.