Made within algorithm variant-aware.

[SVN r86606]
Made perimeter algorithm variant-aware.

[SVN r86619]
[geometry] Fixed self-turn points, neighboring function in get_turns did have the wrong meta-function. Also cleaned corresponding unit tests / added test cases for reported error (reported by Joan on mailing list)

[SVN r86627]
[geometry] fixed self_intersection_points unit test for clang, added missing include

[SVN r86628]
Made remove_spikes variant-aware.

[SVN r86634]