Various fixes 1

These commits fix some detail problems I came across while using three.dart.
Also, they adapt to the latest Dart platform changes.

I tried to keep spaces vs. tabs as they were, but this is quite tedious since Dart Editor does not support real tabs.  Can we agree on dropping tabs?

I further suggest to merge latest into master, because master is the default branch for pub, but master is not usable with a recent Dart Editor/SDK.