Exact geodesic for triangular meshes

Geodesic (shortest path) algorithm for triangular mesh (triangulated 2D surface in 3D).

This is an implementation of exact geodesic algorithm for triangular mesh (first described by Mitchell, Mount and Papadimitriou in 1987) with some minor improvements, extensions and simplifications. The algorithm has O(n^2 \log n) worst-case time complexity, but in practice can work with million-node meshes in reasonable time. For the quick overview, see J. O'Rourke, "Computational Geometry Column 35", SIGACT News, 30(2) Issue #111.