Added computational electrophysiology tests

In these 3 basic tests all Na and Cl ions end up in one compartment
after swapping, i.e. in the second trajectory frame. swap_x tests
swaps in x direction, swap_y and swap_z accordingly. Systems are
identical, just rotated to allow for swaps in all 3 directions.

Run with VERSION 5.0-beta2-dev-20140124-8cad3d196f
where the computational electrophysiology patch has been added.

Change-Id: I6a7db980d12fa2a6eaf490caaca9bb4250aaadcc