tutorials: Renamed .org -> .orig

See http://www.openfoam.org/mantisbt/view.php?id=2076
  - .org is the file extension for emacs org-mode as well
  - .orig is more to the point (.org isn't always recognized as "original")
  - .original is too long, although more consistent with the convention
    of source code file naming

Update script contributed by Bruno Santos

tutorials/mesh/foamyHexMesh/mixerVessel/Allrun-simulation

@@ -18,7 +18,7 @@ runApplication mergeOrSplitBaffles -split -overwrite
 runApplication createPatch -overwrite
 
 # Copy fields after meshing to avoind the generation of unnecessary patch fields
-\cp -r 0.org 0
+\cp -r 0.orig 0
 
 # Initialize alpha
 runApplication setFields