Triangulation_3 fix segment traverser

[lrineau]

Tasks

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1. Question to answer: should the locate types of _cur and _prev always be equal?
2. [Jane] In the simplex traverser, replace all cases with OUTSIDE_AFFINE_HULL by tests of cell_iterator == end(),
3. [Jane] In the simplex traverser, always use ltprev (and never ltnext).
4. [Laurent] Fix those locate types for corner cases (like "outside convex hull", or "target is on a edge/facet"
5. [Laurent] add tests of the traverser with a 2D triangulation
6. Triangulation_3: bug in Triangulation_segment_cell_iterator_3 in 2D #7130
   Bug Pkg::Triangulation_3 +2
   

Note

• When _cur is Cell_handle() then the locate type is meaningless (for the moment, it is OUTSIDE_AFFINE_HULL).
• The locate types of _cur and _prev are always equal, but when _cur is the end (Cell_handle()), or when _prev is Cell_handle().

[lrineau]

We could close this issue. The remaining task, about the 2D issue, is already reported as issue #7130.