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/combustion/PDRFoam/flamePropagationWithObstacles/Allrun

@@ -6,7 +6,7 @@ cd ${0%/*} || exit 1    # Run from this directory
 . $WM_PROJECT_DIR/bin/tools/RunFunctions
 
 rm -rf 0
-cp -r 0.org 0
+cp -r 0.orig 0
 runApplication blockMesh
 runApplication changeDictionary
 runApplication topoSet