Integrating Keystack plugin within MacOSX::Movie

[joseph]

The Keystack plugin seems to be a complete implementation of the idea behind 'keystroke' (which in turn is intended to overcome shortcomings in 'hit').

I'd like to see the _using concept in Keystack dropped in favour of named keys in an options hash argument, but otherwise replacing the keystroke method in MacOSX::Movie class with this more extensive solution.