Put the physics actor to sleep, or wakes it up.
|entity||registered Entity pointer (Actor)|
|mode||0 = wake Actor up, 1 = set Actor to sleep|
1 if successful, 0 otherwise.
If mode = 1, the actor will stay asleep until the next call to simulate, and will not wake up until e.g. a force is applied to it.
pXent_setsleep(my, 1); // set Actor to sleep