some improvements in vector.py
some improvements in vector.py

(mostly cosmetic, but also make sure that the vector storage is not
resizable)

krono/pycket,cderici/pycket,samth/pycket,magnusmorton/pycket,pycket/pycket,vishesh/pycket,pycket/pycket,vishesh/pycket,vishesh/pycket,krono/pycket,magnusmorton/pycket,magnusmorton/pycket,krono/pycket,samth/pycket,pycket/pycket,samth/pycket,cderici/pycket,cderici/pycket