[Gmsh] Suggestion: set the direction of the normal vector of a surface

[Yann COLLETTE]

Hello,

It should be nice to be able to set the direction of the normal of a 
surface in gmsh.
I use code-aster to compute some structural parameters and, sometimes, 
code-aster complains about the direction of the normal of a surface.
To correct this, I find the surface for which I need to change the 
direction of the normal and then do sometimes like this.
I change Physical Surface(98) = {124} into Physical Surface(98) = {-124} 
and it works. No complain anymore.

Yann COLLETTE