Initial test code for the HorizonCulling
Move the GEOPATCH_MAX_DEPTH into GeoPatchContext and then limit the max depth by it instead of hardcoding the number.
Also recalculate the max depth when changing the settings.
Eliminate warning about bool to int comparison
Clip the rendering of the patch according to the HC algorithm.
Still has one outstanding bug.
Merge branch 'master' of https://github.com/pioneerspacesim/pioneer into try_culling
New Plane and Sphere class files.
Merge branch 'master' of https://github.com/pioneerspacesim/pioneer into try_culling
Make the debug build use SSE2 instructions like other builds.
Use SPlane rather than locally defined Plane struct
Fix some stupidity on my part.
Fix the near side clipping bug with the horizon culling.
Disable debugging sphere rendering code.
Made members of GeoPatch private rather than public and provided accessors.
fixup linux Makefile.am
Widen the test to exclude a higher angle.
Merge pull request #3216 from fluffyfreak/try_culling

Added Horizon Culling for planets.