Implement HBodyDefinition.
@hf:transform and @hf:format moved from HFrame to HBody
@hf:condition added to HBody (but not implemented)
HBodyDefinition will return an element instead of a fragment.
This element will be a shallow clone of the element passed when the definition was created.

Transforms should continue to return a fragment.
Their loadTemplate() will now be called with a fragment.
Pass the error detected in script queueing to the error callback.
Test for nested frames.
Implement HFrame#frames[]
HFrame#bodyElement