IO on ghosted meshes buggy

[Jan Blechta]

from dolfin import *
parameters["ghost_mode"] = "shared_vertex"
mesh = UnitSquareMesh(3, 3)
cf = CellFunction('size_t', mesh)
f = XDMFFile(mesh.mpi_comm(), 'cf.xdmf')
f.write(cf)

crashes with

*** Error:   Unable to complete call to function add_data_item().
*** Reason:  Assertion num_items_total == (std::int64_t) MPI::sum(comm, x.size()) failed.
*** Where:   This error was encountered inside /vivid/home/jan/dev/fenics-master/src/dolfin/dolfin/io/XDMFFile.cpp (line 1459).

[Nathan Sime]

I vaguely recall having problems with this from a long time ago with "shared_facet" also. I'll see if I can find an example...

[Jan Blechta]

Issue #846 was marked as a duplicate of this issue.