Cleaned up placement of high-order edge nodes on geometric surfaces

git-svn-id: https://geuz.org/svn/gmsh/trunk@19893 59c8cabf-10d6-4a28-b43f-3936b85956c4
Fixed and cleaned up GFace::closestPoint

git-svn-id: https://geuz.org/svn/gmsh/trunk@19894 59c8cabf-10d6-4a28-b43f-3936b85956c4