[Tinymux] Adding Penn's fmod function

[Stephen Dennis]

I've added FMOD() to the 2.4 cvs. If you have access to that, you
should be able to borrow fun_fmod() from funmath.cpp. There's no
funmath.cpp source file in 2.3.5.24, so put it in functions.cpp.

And, I'm sure you'll remember to add a line for "FMOD" in the function table.

Brazil