I can tell by reading the code that that part of the code ignores other keys (volume and camera keys), what he wants to do is display the GUI that is hidden by LÖVE Android (Just the buttons) but for that you should use a non-fullscreen mode, since fullscreen covers the whole screen including the part used to display the buttons
They putted it in there but then, they said "Lets take it out" so basically it wast really needed, developers can put a button in their applications with "dumb" code. So Google discourages its use (Yeah its the same link, I want you to understand).
Use a gesture, and stop complaining, or buy a new phone maybe...
It's one line?? Then grab the code from the repository implement it and use it in your projects, I think it isn't needed in the port... at all... It's my point of view anyway so Martin will decide