If either signal is detected, we try to terminate gracefully. If we're
given enough time before a nastier signal like SIGKILL is sent, we'll
then be able to finish computing and writing out the current timestep.

If we do not take such precautions, chances are the HDF5 output will be
corrupted.

This is now necessary even though the code is entirely serial.

This works because interpolateP0ToP1 is in dune-fufem now

Prior to this change, dune-tectonic was incompatible with
dune-fufem releases/2.4-2 and later, thus also releases/2.5-1

Prior to this change, dune-tectonic is incompatible with
dune-fufem releases/2.4-1 and earlier

This allows us to remove the last boost::filesystem dependency, and
thus all of boost. It seems to be a better idea than hardcoding the
path to the source directory (which might be unavailable later) anyway

This can be used in conjunction with paraview to interpolate data from
an unstructured, fine grid (on which plotting a vector field would
lead to a mess) onto a structured, coarser grid using the 'Resample
with DataSet' filter.