Make HRRPUL work across meshes

[rmcdermo]

Currently, HRRPUL only integrates across the mesh where the DEVC lives. I think that at this point we need to make this multi-mesh compatible. It is important for diagnostic purposes that we are able to do this easily, and this usually means putting a line of DEVC in the middle of the burner and checking that SUM(HRRPUV*DZ) gives the correct HRR. And we are also wanting more and more to check the grid dependence of HRRPUL(Z) in our attempts to develop grid independent fire growth models.

Here is a simple test case. The burner is 1 m2 and has HRRPUA=100 kW/m2. The _hrr.csv file shows 100 kW. The _line.csv file will integrate to 100 kW if there is 1 mesh. It will integrate to 25 kW if I split the domain into 4 meshes.

test.fds.txt