suzerain: #2979 towards imexop rewrite

Prior work, which should have nailed this, did not.
I may have hosed the banded matrix assembly which may
demonstrably have larger bandwidth.  So while the forward
accumulate00 routine can do the right thing, I suspect
the pack{c,f}00 routines cannot.  Will work towards writing
up the logistics and a way around this all.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44025 0bd85f0b-c151-43b9-a1e9-27231104551f