Before I updated (using 2.76), I had Blender configured such that I could deselect using MOUSE3. For example, I could use C to begin circle selecting, then click MOUSE3 to deselect.
When I updated to the latest Blender version (2.79b), all my rebinds were lost. Blender reverted to its default, which is to use the middle mouse button (MOUSE2) instead of my custom MOUSE3 setup.
I have managed to fix most cases of this by rebinding keys, but I cannot find where to rebind the circle/box deselect functions. They do not show up in User Preferences (the regular circle/box select functions do, but not the deselect ones).
I know this must be possible, because I did it before.
Solutions involving using "Emulate 3 Button Mouse" are not desired; I know I can emulate a middle mouse button, but that is not the goal. The goal is to use a different mouse button in place of the middle mouse button, not to use a combination of keyboard and mouse inputs to fake a middle mouse.