Misc changes include removal of shift warning for no shift and
change in the absorption XS in run_diffusion.py to something more physical.

Minor reduction to the aggressiveness of SDWS-PS.

I forgot what this does.

error with non perfect grids

(red-black)

Need to extend to multigrid next.

Fix implementation of multigrid (especially at bc's).

We now add an extra point at the end for odd grids.

Shows promise for adjoint-weighted collapse with DB^2 added.

Also fix normalization of chi (sometimes it would try to normalize chi even though it's 0)