Merge branch release-2016

Dropped the post-submit change because where we test
with older clang we now always specify a suitable
status for openmp.

Change-Id: I993da20856861c0b8a0888f7fa0deed8853349a8

diff --cc src/gromacs/gmxlib/nrnb.cpp
Simple merge

diff --cc src/gromacs/mdlib/trajectory_writing.cpp
Simple merge