Merge branch 'v2.3' of https://github.com/plumed/plumed2 into v2.3

.travis.yml

CHANGES/v2.2.txt

CHANGES/v2.3.txt

VERSION

configure

configure.ac

macports/Portfile.in

macports/generate-portfile.sh

patches/gromacs-2016.3.config

patches/gromacs-2016.3.diff/src/gromacs/CMakeLists.txt

.../gromacs-2016.3.diff/src/gromacs/CMakeLists.txt.preplumed

patches/gromacs-2016.3.diff/src/gromacs/mdlib/force.cpp

...gromacs-2016.3.diff/src/gromacs/mdlib/force.cpp.preplumed

patches/gromacs-2016.3.diff/src/gromacs/mdlib/minimize.cpp

...macs-2016.3.diff/src/gromacs/mdlib/minimize.cpp.preplumed

patches/gromacs-2016.3.diff/src/programs/mdrun/md.cpp

...s/gromacs-2016.3.diff/src/programs/mdrun/md.cpp.preplumed

patches/gromacs-2016.3.diff/src/programs/mdrun/mdrun.cpp

...romacs-2016.3.diff/src/programs/mdrun/mdrun.cpp.preplumed

patches/gromacs-2016.3.diff/src/programs/mdrun/repl_ex.cpp