[Amibe] RemeshPolyline: fix some Dichotomy failure

This bug was not visible in debug mode and this commit should not change
any thing but it does. So I suspect a JIT inlining bug.
[Amibe] remesh.py: disable multi-threading in afront

afront is slower on 8 processors than on 1 processor probably because of
multi-threading is implemented at a too low level and synchronization eat
all the time.
[Amibe] RemeshSkeleton: swap around inserted vertices
[Amibe] VertexSwapper: default group=-1 and support non manifold vertices
[Amibe] Fix trove 2 to trove 3 migration (again)

Fix commit 1d50857 (Switch from GNU Trove 2 to 3)