the component does not use reflection, only public properties. here we also want private ones, in case somebody did not follow code style and has a mapping `children` but the method `getAllChildren` for example.

the next step would be to optionally use the phpcr node to get even unmapped children, but i leave that to @dantleech new tree bundle some day. this PR is a minimal fix for the problem i encounter in my project that i don't see children in some tree widgets.