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.