This reverts commit 37001778.

This reverts commit 8dab6d81.

(sorry)

It now detects if different replicas have different bias-factor

* Marco De La Pierre: added WALKERS_DIR option for WALKERS_MPI

* Marco De La Pierre: WALKERS_DIR option for WALKERS_MPI, not for single replica runs

* Marco De La Pierre: WALKERS_DIR for multiple walkers metad made general

[makedoc]

Dimer CV

* Citation fixed as suggested
* Added PBC-friendly virial contributions: compared with the numerical derivatives
  for a configuration and the same with a dimer shifted by the lattice vector on one of its components.

This is required since intel compiler does not have complete c++11
support but still works correctly.

Perhaps we have to find a way to include intel compiler on travis
so as to be sure we do not include unsupported c++11 features.

[makedoc]