when installing from PyPI, to avoid cython dependency.
- Using python 2 to create the cpp file uploaded on PyPI (this will change to python 3 in 2.6, see \issue{502}).
- Module VES: Fixed a bug in updating of bias potential in \ref VES_LINEAR_EXPANSION that is present for certain integrators that call the calculation of the bias multiple times (see [here](https://groups.google.com/d/msg/plumed-users/kPZu_tNZtgk/LrkS0EqrCQAJ)) and replica exchange.
