Parallel bug on reals with PETSc 3.9+

[Sebastian Mitusch]

The following works in parallel with PETSc 3.8, but fails with a segmentation fault with PETSc 3.9 and 3.10.

from dolfin import *

mesh = UnitCubeMesh(50, 50, 50)
R = FunctionSpace(mesh, "R", 0)
assemble(TestFunction(R)*dx)

Note that for smaller mesh sizes (30 x 30 x 30 cube for instance) the example runs fine.