nosetests needs rednose

[MathieuLeocmach]

Following Readme.md instructions, I installed PERI on a new machine and wanted to run the tests with
nosetests, but had the error message

  nosetests: error: Error reading config file 'setup.cfg': no such option 'rednose'

It was solved by installing rednose.

I suggest to include rednose in the dependencies of PERI.

[MathieuLeocmach]

To complete tests, package vtk is also needed. It should be included in the dependencies of PERI.

Also, the broken line 238-239 in peri/interpolation.py makes doctest fail. The two lines should be merged.

[briandleahy]

Hi Mathieu,

Thanks for the heads-up on the tests. The broken line in interpolation should be fixed in commit d3d7d48 on the develop branch.

As for the missing rednose and vtk requirements from peri -- right now for some reason the requirements.txt file is empty, since commit 1b9ccd8 "changing packing for pypi". @mattbierbaum is the requirements file empty for a reason?

For now, Mathieu, vtk is only used to render images and isn't important for peri (it should be an optional dependency), so don't worry about the vtk imports failing.