Update PETSc monitor code for changes in PETSc dev

[Prof Garth Wells]

Monitors have been disabled to keep DOLFIN compiling against PETSc dev. Need to be fixed.

[Lawrence Mitchell]

I think the problem is that PETSC_VIEWER_STDOUT_(...) does not increase the refcount of the returned viewer. So you should not call PetscObjectDereference on the viewer you get back after creating the PetscViewerAndFormat.

[Prof Garth Wells]

@pefarrell Can you fix this issue?

[Prof Garth Wells]

@wence Can you help us to understand why something so simple (print residual to stdout) requires so many lines of code?!

[Lawrence Mitchell]

Not really sure. I think this is designed to be sort of internal to petsc and you just call Snessetfromoptions with the appropriate options set.

[Patrick Farrell]

Garth: I've committed a fix to pefarrell/fix-petsc-monitors. It passes all regression tests (finally).

[Anders Logg (Chalmers)]

Removing milestone: 1.7 (automated comment)