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When transfering constraints to coincident points on deletion of geometry, a tangency/perpendicular constraint
cannot be blindly transfered as the destination edge may not be tangent/perpendicular leading to unexpected behaviour.
However, the user does expect that something that was coincident with such end-to-endpoint constraint (which implicitly includes a coincident constraint)
remains coincident after deletion. Therefore, the change of type to coincident.
This implicitly solves the problem of representation of constraints leading to a crash in coin3d.
fixes#3291
952aaa458e