Merge branch 'v2.6' of https://github.com/plumed/plumed2 into v2.6

CHANGES/v2.5.md

regtest/ves/rt-md_le-1d-fourier-shifted/Makefile

...est/ves/rt-md_le-1d-fourier-shifted/colvar.data.reference

regtest/ves/rt-md_le-1d-fourier-shifted/config

.../ves/rt-md_le-1d-fourier-shifted/histogram.data.reference

regtest/ves/rt-md_le-1d-fourier-shifted/input

regtest/ves/rt-md_le-1d-fourier-shifted/plumed.dat

...est/ves/rt-md_le-1d-fourier-shifted/pot_coeffs_input.data

...md_le-1d-fourier-shifted/pot_coeffs_output.data.reference

.../ves/rt-md_le-1d-fourier-shifted/potential.data.reference

src/ves/MD_LinearExpansionPES.cpp