Switch to std::set for global dofs (since it will be small).
Fixed flacky performance in FunctionAssigner for different combinations
of MixedSpaces.
Comment out changes to keep entity dofs on same process - check if 32-bit buildbot passes
Re-enable facet with distribution of dofs.
Merge branch 'garth/dofmap-reordering-speedups'
Merge branch 'johanhake/dof-reordering'

Conflicts:
	dolfin/fem/DofMapBuilder.cpp