[Bf-python] Small omitted functions

[Campbell Barton]

This is the world.makeActive() function- Needs to be added to World.c in 
the Python Dir, its quite simple, as for mist- This can be toggled with 
the mode- setMode and getMode

Its just not documented yet.

- Cam

/* world.makeActive */
static PyObject *World_makeActive (BPy_World *self)
{
    World *world = self->world;
    /*If there is a world then it now has one less user*/
    if(!G.scene->world) G.scene->world->id.us--;
    world->id.us++;
    G.scene->world = world;
    Py_INCREF(Py_None);
    return Py_None;
}
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