Bugfix in UGGridIdSet::id method for facets of 3d elements

The Dune grid interface requires that copies of entities on different levels have the same id. The UGGridIdSet failed to implement this in the 'id' method for codim-1 faces of 3d elements. I am afraid I omitted that out of pure laziness back in the days when I wrote that code.

The commit also adds a simply unit test that would have caught the bug.

added 4 commits

• 7fce8883...c7b628b9 - 3 commits from branch master
• 7368fb0c - Bugfix in UGGridIdSet::id method for facets of 3d elements

Compare with previous version

merged

mentioned in commit e2bb0eef

picked the changes into the branch cherry-pick-e2bb0eef with commit b09cdf51

mentioned in commit b09cdf51

mentioned in merge request !435 (closed)

picked the changes into the branch cherry-pick-e2bb0eef-2 with commit ff978c76

mentioned in commit ff978c76

mentioned in merge request !436 (merged)

mentioned in issue infrastructure/issues0#65 (closed)