Add a few debug asserts to GFX frame building code

Turns iloops into quick aborts in the case where we try to add a frame as its own child. Yes, this happened to me.
Fix error message for exception in EventDispatcher#dispatchEvent
Bug 1066566 - Re-enable loading initial SWF from an ArrayBuffer

This broke in the nat refactoring
Bug 1066566 - Fix the "Open File" button in the Inspector
Merge pull request #1707 from tschneidereit/master

[Bug 1066566] Fix inspector's "Open File" functionality