A way of explicitly reporting exceptions

[C. Scott Ananian]

I am ambivalent about where it goes; it depends to some degree with
how the feature is implemented.

`setTimeout(function() { throw e; }, 0);` is ugly, but it seems to
have most of the behavior you want.  There are similar mechanisms with
promises and jobs that could be used.  I believe Allan said that the
"use the standard uncaught exception handler" behavior is already in
the standard.  If we're talking about tweaks to make this approach
more palatable (`Promise.throw(e)` ?) then the ES6 spec is
appropriate.

Alternatively, one could view this as part of the `console`
functionality, since what seems to be wanted is simply easier access
to the debugging capabilities of modern web consoles, like the
already-existing `console.trace(message)` which prints `message` along
with a stack trace.  (And some people want to be able to pass
additional flags to have certain special behaviors in a debugger.)
That would belong on the DOM side (or wherever the cross-platform
`console` spec is kept).

Finally, it hasn't been discussed much, but some platforms provide
explicit access to the 'uncaughtException' handler.  In python this is
[`sys.excepthook`](https://docs.python.org/3/library/sys.html#sys.excepthook)
and in node this is [an `uncaughtException` event on the process
object](http://nodejs.org/api/process.html#process_event_uncaughtexception).
If we wanted to standardize something like that I'm not sure which
spec that would belong in.
  --scott