This is a copy of complex/fe_test, changing
* from group to Verlet cut-off scheme,
* from leapfrog to vv
* rvdw from 1.2 to 0.9 to match rcoulomb
* nstlist increased from 5 to 10, and
* t-coupling from Berendsen to v-rescale.

It should be an effective test of FEP list build, exclusion of FE
pairs from the normal lists, and the PME grid correction.

It differs from nbnxn-free-energy only in the integrator.
