Add ensureBehaviors() to detachBehavior*()

Need to add ensureBehaviors() to detachBehavior*().

The intent may be to detach behaviors defined in behaviors().
In the original implementation, if these behaviors() are not yet attached, they can not selectively be detached.
Merge pull request #136 from mdeweerd/patch-1

Add ensureBehaviors() to detachBehavior*()