A bunch of DOM changes we'll need to support the new yahoo mail
and ATLAS stuff; this is neccessary but not sufficient, since they
also heavily use setters/getters, which I am not sure we want to support in 3.5.x...
(But this stuff is standalone)

1. Provide some emulation of mozillaisms like Node.prototype = ... .
These are incomplete, but should hopefully cover the important stuff.
Related to that, fix HTMLDocument to use a proper prototype.

2. Merge from Apple's tree: support the no-op debugger; statement,
it at least seems to be used by yahoo...

3. Readonly support for characterSet property.

4. Fix crash on reading some properties of mouse events that weren't
dispatched --- noticed on testing this stuff.