Extended pysal.weights.user.build_lattice_shapefile 

Differs from the linked GIST in that this PR (1) uses round() to try to avoid topological issues and (2) pushes the hexagon to a PySAL polygon object.

![sample](https://f.cloud.github.com/assets/2105468/2284096/b5ffb702-9fc5-11e3-82ae-aa6a7ad2d5f5.png)