add Neumann and Dirichlet bcs to demo-dg-poisson
change n and h in Poisson.ufl
Fix doctest for mixed-poisson-dual.
Merge branch 'martinal/topic-fix-mixed-poisson-dual-doctest'
Fix Issue 274.
Minor changes.
Merge branch 'mirok/fix-issue-271'
Merge branch 'garth/fix-issue-274'