Add recipe for gmsh.

Add a recipe for gmsh (http://geuz.org/gmsh/) 2.8.4.

The GUI part depends on FLTK, which isn't in the recipe repository.  I mostly use gmsh in the batch mode and doesn't need GUI at the time being.  A binary file can be found at https://binstar.org/yungyuc/gmsh/2.8.4/files, which was built on OSX 10.9.