make F4 useful

[zmike]

Not sure if this is desired after so many years of having F4 do something else, but it's the only feature epsxe has that's still superior to pcsxr in every way, and I have a hard time playing games without it. Feel free to reject, I just thought it might be worth considering bringing into the core repo.

Windows changes are tested, linux changes compile, so probably they work.