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sudo defaults write /Library/Preferences/com.apple.windowserver DisplayResolutionEnabled -bool YES;
sudo defaults delete /Library/Preferences/com.apple.windowserver DisplayResolutionDisabled;

// by the way, you need to logout and log back in for this to take effect.  Or at least that's what
// Quartz Debug says.  Who knows, maybe it's lying?

// P.S. Go to [Apple menu --> System Preferences --> Displays --> Display --> Scaled] after logging
// back in, and you'll see a bunch of "HiDPI" resolutions in the list to choose from.