This one is a bit tricky...

1. The is_darwin() will resolve to true on the native build. It will also resolve to true on MacPorts. However, there is not 3.x build for MacPorts (I'm not sure about Brew)
2. What I intend to do is to further improve the is_darwin method so that it checks if it's running on Quartz instead of checking just the OS. This is why I created it as a separate method in conf and didn't check for the OS within the meldwindow.py
3. Merging the patch will allow others to help me out on this.

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