Partitioning fails on 2D geometries

[davidscn]

When trying to use the mesh partitioner for a 2D geometry, I face several issues such as:

partition_mesh.py:201: RuntimeWarning: invalid value encountered in true_divide
  axis /= np.linalg.norm(axis)

or

line 301, in partition_uniform
    small, big = greedy_choose(prime_factors(numparts))
TypeError: 'staticmethod' object is not callable

I realized that these are mostly untested things. We should add tests for the partitioning and fix the problem here. The mesh to reproduce this issue:
2D-example.zip

[kursatyurt]

Static method error is due to inner functions it would fixed in #114.

The top one other Nan/Inf error which would arise is due to weakness of the algorithm used (or may be just implementation), I would suggest to use METIS partitioner.