Merge branch 'test-shapefunction-duality' into 'master'

Andreas Dednerrequested to merge
cherry-pick-adb16631 into releases/2.6

Test shapefunction duality

See merge request !62 (merged)

(cherry picked from commit adb16631)

546930ea Remove redundant LocalInterpolation test f6a0792b Rewrite testLocalInterpolation to match Ciarlet's definition

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