Update of cad/gmsh port

[Stephen Montgomery-Smith]

I have attempted to update the gmsh port to version 2.4.2.  This is 
quite a large change, because gmsh has changed from using configure to 
cmake.

I'll submit the port in due course, but since this is the first port I 
have ever updated using cmake, I thought I would ask for comments first.

In particular, I had to hack quite a bit to make NOPORTDOCS be respected.

You can find the updated port at 
http://www.math.missouri.edu/~stephen/gmsh.tar.gz

Pedro: the binaries mshsort and dxf2geo no longer seem to be built.  I 
hope that these weren't something special you needed.

Thierry: I haven't yet tested the WITH-OCC option yet.  I am still 
waiting for opencascade to finish building.

Stephen