Explicitly reset the _children array in Backbone.Component._removeChildren().  In cases where the added child is not a Backbone.Component, there is no guarantee for a wrapper around remove() which also means that the child reference is not guaranteed to be removed from _children.
Simplify empty() test for non-Backbone.Component children to use Backbone.View instead of custom component.
update documentation
Merge branch 'master' into gh-pages