Bug 824589.  Convert XULElement to WebIDL.  r=peterv

The assertions in nsINode and nsWrapperCache are to eagerly catch
failures to override those methods.

The classinfo change for XULTreeBuilder is needed because one of those
is returned via an nsIXULTemplateBuilder attribute on XULElement.
Alternately, I could mark it notflattened in Bindings.conf, but Enn
said he prefers this anyway.

The change to the QI impl in BindingUtils is needed because when
XPConnect converts an IID from C++ to JS it makes is an nsJSID, not an
nsJSIID.  We've run into this before, sadly.

I removed "id" from nsIDOMXULElement because it's already on Element.
I suppose I could have left it there, but this seems cleaner.

The nsJSIID::HasInstance changes are needed to support XBL-implemented
interfaces.  Sadly, this does mean that if the underlying object QIs
to something but we didn't put those props on the WebIDL we'll end up
testing true for instanceof but not exposing the props.  I don't see
an obviously better way.  We should work on killing off uses of
"instanceof someinterface".

The browser.js change is needed to avoid throwing exceptions during
browser-chrome tests that are now getting reported because our
swapFrameLoaders is no longer an XPConnect method.
Bug 829867.  Unpref PaintRequest and Screen WebIDL bindings and remove some cruft from quickstubs.  r=peterv

nsIDOMCharacterData and nsIDOMText quickstubs are not needed after bug 826703.

nsIDOMRect quickstubs haven't been needed since bug 824970 landed.

nsCSSPropertiesQS has been unused since bug 801083 at least.

The various includes being removed are either fully on WebIDL now or using WebIDL quickstubs.