Check reprojections.

This merge request builds on @ahopkins1 ah-48 branch and associated issue#48. I've updated the original code to check the reprojections. It not only checks for inf values but also empty geometries, invalid geometries, and whether the grid file used to calculate the reprojection is available. The latter is something I think led to many of the issues we were seeing where our firewall was preventing the reprojection from taking place.

This also led to reorganizing where the _make_valid() method is used. I moved the method to utils.py, and made sure it was calculated before the repojections, and the testing of the reprojections. This eliminated a lot of duplicate code.

Finally I added test_reprojection to test the new functionality.