Allow catch surpressed errors

[sean-roberts]

Facebook for example overrides the window.onerror function. It could be useful/interesting/fun to override that function before/after the client scripts override it so we could bring to light any, typically suppressed, errors.

[sean-roberts]

One interesting thing that could be added is to have the toString() call return the original override's string representation. Just in case there are any dirty checks for that or so that we can try to be as not invasive as possible.