valgrind tests for geometry.c

There are actually no memory leak bugs or invalid accesses in geometry.c. There *was* a docstring that was incorrect about the shape of one of the arrays though. The python wrappers supply the correctly-shaped arrays, it was just the docstring that was wrong.

Anyways, I figure it's a good idea to commit the machinery for these tests -- it's totally separate from any python testing, but would have caught the RMSD bug that I fixed last night.