Rename PIO::nc -> PIO::m_nc.
Clean up the TR1 business a little bit.
Most PIO methods don't return PetscErrorCode.
Merge branch 'dev' into new-error-handling
Use a shared_ptr to manage PIO::m_nc.
Some PIO methods use return values...

...instead of using output arguments.
Use new PIO method signatures in the rest of PISM.