[petsc-dev] setting viewer format from options

[Hapla Vaclav via petsc-dev]

I need to distinguish a PetscViewerFormat in DMLoad() and MatLoad(). And it 
would be handy to be able to set it from options. So I wanted to add 
-viewer_format option into PetscViewerSetFromOptions().

But the problem is PetscViewerSetFormat() is deprecated and 
PetscViewerPushFormat() needs to be paired with PetscViewerPopFormat() which I 
don't know where to place correctly.

Can you see some clean way to proceed?

Thanks

Vaclav