Fixed partial_tempering with gromacs 5 convention. Old behavior can be
forced with --gromacs4 option.

make clean was not correctly cleaning plumed executable

Thanks to Qingh Liao

correct definition of G vector in the documentation. A 1/gamma factor was missing. The actual calculation was correct and it remained unchanged.

I noticed that cache is not saved if brew is removed
(apparently some travis tool requires a brew library)

ERMSD now gives the same results irrespectively of units.

The value of PLUMED_ROOT stored in statically patched MD code was
incorrectly set to the compilation directory rather than the installed one.

The only way to trigger the bug from regtest was by observing the behavior
of rt-make-exceptions when plumed was installed by macports (since in this
case the compilation directory is removed).

Messages related to NOPBC keyword were wrong

Thanks to @valsson

Includes mention to ABIN code

See https://groups.google.com/d/msgid/plumed-users/8fcca53b-38d1-470e-a413-a4339702c6db%40googlegroups.com

Thanks to Qingh Liao

osx8.2 is deprecated.

Problem was likely due to an upgrade of mpi in homebrew on travis

There was some "return 1". Now that exit code is checked, this would
have triggered an error

Report a failure in the following two cases:
- unknown test type
- test program exiting with non-zero code