Fixes regression in childViewLayout

This PR fixes a regression introducted by https://github.com/sproutcore/sproutcore/commit/ea620753a313f085460de2ba preventing childViewLayout to work.

I've added unit tests for childViewLayout to avoid this kind of problem in the futur.
Note that I've also added unit tests for https://github.com/sproutcore/sproutcore/pull/1123 which is not commit in master yet.