Pickling for the old CDF vector class.

AUTHORS:

• Jason Grout

TESTS:

sage: v = vector(CDF,[(1,-1), (2,pi), (3,5)])
sage: v
(1.0 - 1.0*I, 2.0 + 3.14159265359*I, 3.0 + 5.0*I)
sage: loads(dumps(v)) == v
True