added comment: tetgen can lead to incorrect meshes for non manifold geometries

doc/TODO

-$Id: TODO,v 1.65 2007-10-14 09:51:17 geuzaine Exp $
+$Id: TODO,v 1.66 2007-11-12 10:48:17 colignon Exp $
 
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@@ -8,6 +8,13 @@ entity, and sort like in post-processing.
 
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+fix tetgen for non manifold geometries: with a single surface
+connected to a volume and tetgen modifies the volume boundary mesh, we
+get hanging nodes
+Plus we need to fix the 1D mesh in all cases
+
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+
 add way to invert element orientation (per element or per surface)
 
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