Merge branch 'v2.1-hrex' into v2.2-hrex

patches/gromacs-4.6.7.config

patches/gromacs-4.6.7.diff/src/kernel/md.c

patches/gromacs-4.6.7.diff/src/kernel/mdrun.c

patches/gromacs-4.6.7.diff/src/kernel/repl_ex.c

patches/gromacs-4.6.7.diff/src/kernel/repl_ex.h

patches/gromacs-4.6.7.diff/src/kernel/repl_ex.h.preplumed

regtest/basic/rt-hrex-0/Makefile

regtest/basic/rt-hrex-0/config

regtest/basic/rt-hrex-0/out.reference

regtest/basic/rt-hrex-0/processed.top

regtest/basic/rt-hrex-1/Makefile

regtest/basic/rt-hrex-1/config

regtest/basic/rt-hrex-1/out.reference

regtest/basic/rt-hrex-1/processed.top

regtest/basic/rt-hrex-2/Makefile

regtest/basic/rt-hrex-2/config

regtest/basic/rt-hrex-2/out.reference

regtest/basic/rt-hrex-2/processed.top

regtest/scripts/run

scripts/partial_tempering.sh