Subclass TextViewer to add mock methods instead of monkey-patching it.

Patch by Steve Dougherty.

That option had been for Win2k compatibility (which was dropped with
Python 3.3) and makes default ttk ugly on post-Win2k systems.

- Nix the 'noxp' option, it was for Win2k compatibility (which was dropped
  with Python 3.3) and made default ttk ugly on post-Win2k systems (#21665)
- Use 'OPTS=symbols' instead of 'DEBUG=1'; symbols is the official method
- Use core, shell, dlls, install-binaries, and install-libraries targets
  instead of all and install to avoid trying to 1) build packages that don't
  work with MSVC 10+ and 2) install unnecessary bits and pieces.

Add BaseEventLoop._closed attribute and use it to check if the event loop was
closed or not, instead of checking different attributes in each subclass of
BaseEventLoop.

run_forever() and run_until_complete() now raises a RuntimeError('Event loop is
closed') exception if the event loop was closed.

BaseProactorEventLoop.close() now also cancels "accept futures".