Would like a safe version of vectorops set_magnitude

[rchristie]

set_magnitude gives a division by zero if v is a zero vector:

def set_magnitude(v, mag):
    """
    return: Vector v with magnitude set to mag.
    """
    scale = mag / magnitude(v)
    return mult(v, scale)

Could either change the above to the following or make it a separate function set_magnitude_zero():

old_mag = magnitude(v)
if old_mag > 0.0:
    return mult(v, mag / old_mag)
return copy.copy(v)

[rchristie]

Same could be said for normalize()