plumed patch -e accepts a close match

When doing plumed patch -e gromacs2016.5 a match with e.g. gromacs2016.4
will be accepted (and issue a WARNING). Useful for automatized patching
procedures.

For instance, in gromacs-plumed package of MacPorts it won't be necessary
to synchronize the Portfile with the exact plumed version.