Fix parsing for grid spacing with type long double

[franzpoeschel]

Mesh.cpp has an explicit instantiation for long double grid spacings:

template
Mesh&
Mesh::setGridSpacing(std::vector< long double > const & gs);

This is important for our Python API as floats default to long double there:

temperature.grid_spacing = [1.0, 1.0]

Result of that:

  long double  /data/9/meshes/temperature/gridSpacing       attr   = {1, 1}

But upon trying to open that Series again:

  Unexpected Attribute datatype for 'gridSpacing'

Because our reading routines only check for float and double.

First commit: Failing test
Second commit: Fix

We should maybe scan our codebase for similar errors.

[franzpoeschel]

Python seems to be really committed to using long double, I'm finding no way to force it to another datatype:

temperature.grid_spacing = np.array([1, 1], dtype=np.double)

Even this one creates long doubles. This could mean that it is currently impossible in our API to specify a dataset's grid spacing in Python.

[franzpoeschel]

It looks like the CI is again in a mood

[ax3l]

Thanks a lot!