Fix issues with window load events.

Window load events are supposed to be dispatched on the window with the target
set to document and the currentTarget set to the window.

Fixes issue 76
Fix issue where getShadowTree was not prefixed with scope.

This also fixes issue where inSameTree was broken as well as returning too
early in case retargetting resulted in target and relatedTarget being the same

Fixes issue 71
Merge pull request #78 from arv/get-shadow-trees

Fix issue where getShadowTree was not prefixed with scope.
Merge branch 'window-on-load' of https://github.com/arv/ShadowDOM into arv-window-on-load

Conflicts:
	test/events.js