Allow either okay or accept_role to be returned by QtConsole confirm exit.

I am using Python 2.7.8 and PyQt 4.10.4 on Linux Mint 17 32 bit, and the latest master de3c13ca6e16aaa0624cfe007e3e326077991670.  When I close a QtConsole using the `X` button, it was not triggering the widgets to close.  When I clicked "Quit", it was returning `0`, which corresponds to `AcceptRole`.  
This problem was preventing the `do_shutdown` method of the [octave_kernel](https://github.com/blink1073/octave_kernel) from being called.