Fixed GB interactions for release-4-6

Fixed GB interactions for release-4-6

Release-4-6 was not using the correct GB kernels,
but the non-GB electrostatics cutoff kernel. In addition,
the accelerated kernels unrolled more than a factor 2 had
a bug that caused a small error in the forces. Both these
issues have been fixed, and the GB results now match
release-4.5.
Note: The GB _radius_ calculations are still only done
in C, but the accelerated options will be re-enabled in
a pending patch (separated for clarity).
Fixes #1096.

Change-Id: I40151b9a9f1920006bfe9a39a8719698a824bfac

fix

Change-Id: I45630252d6a9c05a7f3695a7e6d07dcd13e0a25c