use ViewportParams::screenCoordinates() directly
const'ify
enable antialiasing based on map quality

* fixes regression introduced in commit d0851c32a1e5ead6155dbe4eea741f5769ffb931
[API change] determine clipping automatically

There is no explicit way any longer to enable/disable clipping. Any such code can be removed.
construct a GeoDataLineString
resolve some code duplication
introduce MarbleView
introduce MarbleGLView
introcude GlLayerInterface
clear depth buffer between layer rendering
TextureLayer
PlacemarkLayer
introduce triangulation algorithm for polygons

* taken from http://www.crystalspace3d.org/svnroot/crystal/CS/trunk/{include/csgeom/triangulate.h, libs/csgeom/triangulate.cpp}.
GeometryLayer
introduce GeoGraphicsScene::GlTile and use glDrawElements
adapt PlacemarkLayout
use shaders
GLRenderer