QDialog::keyPressEvent does not support Cmd-Period under Cocoa

QDialog::keyPressEvent looks for Cmd-Period on the Mac, treating it as a shortcut to invoke reject(), as per Escape.

However this keystroke is special-cased by Cocoa, and is never sent directly to applications (so will never be received by QCocoaView:keyDown).

Instead QCocoaView needs to handle cancelOperation: to catch this action, and probably process it by generating a synthetic Cmd-Period keystroke.