tweak


git-svn-id: https://geuz.org/svn/gmsh/trunk@18123 59c8cabf-10d6-4a28-b43f-3936b85956c4
draw volume mesh


git-svn-id: https://geuz.org/svn/gmsh/trunk@18124 59c8cabf-10d6-4a28-b43f-3936b85956c4