Naming of the complex diagonal matrix class.

[John W. Eaton]

On  9-Mar-2009, Jason Riedy wrote:

| It may be too late to change, but would a patch to make complex
| diagonal matrices into diagonal complex matrices be accepted?
| Was where a reason why they were named differently that sparse
| complex matrices?  I've been making that typo far too often...

These names are not new, so we should probably not just change
them as that would force a lot of code to change.  If we decide to
change the names, would typdefs work to preserve the old names?

If we do decide to change the names, I would like to consider a larger
renaming, to use names like  perm_matrix and diag_matrix instead of
PermMatrix and DiagMatrix, and I'd like to do this at the same time as
adding namespace(s) to contain all thes names.

I think any change like this should happen after 3.2.

jwe