Fan Duct for Prusa i3 Rework jhead/e3d

Modified duct to allow mounting to this extruder. Still takes a 40mm fan.
Made to work with a J-Head, but will work with AluHotend and other slender hotends. MAY work with e3d, but not tested.
Keeps the airflow away from the print too and stays out of the way of the main cooler.
You will also need "i3_Fan_Mount-Extended.stl" from http://www.thingiverse.com/thing:967268/#files