Fixed two PME issues with MPI+OpenMP

Change 272736bc partially fixed #1388, but broke the more general
case of multiple MPI communication pulses in PME. Change 272736bc
incorrectly changed tx1 and ty1. This change has been reverted.

Change 27189bba fixed the incorrect PME grid reduction with multiple
thread grid overlap in y. But it broke the, much more common, case
where the y-size of the PME grid is not divisible by the domains in y.
This change, incorrectly, changed buf_my.

Now buf_my is set to the correct value, which solves both issues.

Fixes #1578.
Refs #1388 and #1572.

Change-Id: Id2d7d013a3b8cdc04eda1fb026567088a38ec81f
Version bump after 4.6.7

Change-Id: I1f2e73c2b94f31b67e65bf7cf188fb542391ab4d
Fixes issue with vsiten and verlet buffers.

A loop counter for a loop over vsiten did not take into
account that multiple entries make up one vsiten
particle. Part of #1579.

Change-Id: Ic9a79e89ea9ef8f9f529c9d4a6c5cf05f65e9c7d
Fix malformed CUDA version macro check

The CUDA_VERSION macro check is incorrect in two places. The first is
harmless as it is related to legacy CUDA 3.2 version's reporting. The
second occurrence affects the check that enables stream priorities and
due to the incorrect check, with CUDA 5.5 priorities have not been used.

Fixes #1594

Change-Id: Icf781d41549c39b6b913c11bb11d4dc4e9f3be9c
Merge remote-tracking branch 'gromacs/release-4-6' into release-4-6_ASFeature
add option to modify box-z to trjconv

The new option -boxz allows to write new box coordinates in z-direction
while leaving the lateral box dimension intact. This is especially
useful for changing the box corrdinates of trajectories with lateral
pressure coupling.