WARNING: be careful before pulling petsc-dev!

[Barry Smith]

  I have made a major change to the Vec and Mat internal
data structures. PetscMap() is NO LONGER a PETSc object,
it is now a simply data structure in the Vec and Mat objects.
The m,M,n,N, rowners,rstart,rend, cstart and cstart fields
in the Vec and Mat objects are removed, instead the fields
in the map data structure inside the Mat and Vec are used.

  Aside from the missing PetscMap, this has not introduced
any API interfaces.

  Making this change, almost for sure, introduced some 
errors (making the substantial code changes was painful and
prone to error). Please track down the problems or let
me know about them so we can eliminate the introduced problems.
The external matrix packages have NOT been tested
(they will be tested in nightly builds). 

  Thus, if you are trying to get work done, instead of
tracking down our bugs, I recommend not pulling petsc-dev
for several days.

  Thanks for all your patience,

   Barry

Yes, these code cleanups are painful, but they are
also crucial to the long-term viability of PETSc.