[Gmsh] Subtraction of volumes

[Geordie McBain]

> I’d like to subtract a volume from another one using gmsh. Although this
> operation isn’t difficult to perform numerically, I haven’t found any
> similar command. Unfortunately, the delete command does not adjust the
> boundary.

A similar query earlier this week received the reply: `Use a CAD motor
for creating your geometry and import
it in Gmsh for meshing.'

http://www.geuz.org/pipermail/gmsh/2011/006584.html

I'm finding FreeCAD pretty good for this kind of operation.  Export as
BRep and then Merge in Gmsh.