cc @HanatoK I fixed the problem. Namely, plumed was linking by mistake
another boost version (homebrew).

HomeBrew boost was linked by mistake.

changed some interfaces to return a unique_ptr

Not complete yet

osx8.2 is deprecated.

conflicts arising from the fact that master branch had python_bin added
in the same place where v2.4 had mpiexec added.

I think it is better NOT to recommend sourcing "sourceme.sh". Most users
should install plumed with the canonical procedure (make install)

Notice that this breaks previous "check" target, that I think
was anyway useless.

check: does the check with the non-installed plumed
installedcheck: does the check with the installed plumed

In case MPIEXEC was passed at configure time, it is used.
In case not, env var PLUMED_MPIRUN is checked (for backward compatibility).
Otherwise, `mpirun` is used.

Can be retrieved with

plumed config mpiexec

Added patch for QE 6.2

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

cc: @ralf-meyer

Minor fixes of eABF module