Some minor corrections to the navigation tutorial. Added code example on how to use the opposite_halfedge_handle() function.

git-svn-id: http://www.openmesh.org/svnrepo/OpenMesh/trunk@232 fdac6126-5c0c-442c-9429-916003d36597

Doc/Examples/nav_code4a.cc

@@ -0,0 +1,7 @@
+// Get the halfedge handle of i.e. the halfedge
+// that is associated to the first vertex
+// of our set of vertices
+PolyMesh::HalfedgeHandle heh = mesh.halfedge_handle(mesh.vertices_begin().handle());
+
+// Now get the handle of its opposing halfedge
+PolyMesh::HalfedgeHandle opposite_heh = mesh.opposite_halfedge_handle(heh);