OLCTriangle: optimise triangles with start/end on a leg.

This adds a fourth edge to the triangle solver, such that a triangle
trace can start/end somewhere on a leg.

This seems to work pretty well on many flights (e.g.
http://www.skylines-project.org/flights/482/ or
http://www.skylines-project.org/flights/99/)
but still failes on others (http://www.skylines-project.org/flights/520/)
AnalyseFlight: increase trace size

Needed to yield a better result of the triangle optimisation,
test with flight http://www.onlinecontest.org/olc-2.0/gliding/flightinfo.html?dsId=2267050