Associates a function to an action as a global callback.
This function should not be used by new applications, use it only for global callbacks. For regular elements use IupSetCallback instead.
Notice that the application or libraries may set the same name for two different functions by mistake. IupSetCallback does not depend on global names.
Icallback IupSetFunction(const char *name, Icallback func);
name: name of an action.
func: address of a C function. If NULL removes the association.
Returns: the address of the previous function associated to the action.