MK8 heatsink fan shroud / print cooler

Uses the heat sink fan of the MK8 extruder to also do active cooling of the print. This is a remix of http://www.thingiverse.com/thing:22297 because my extruder head orientation and dimensions were somewhat different and the original design would not fit.

This version is 11mm thick, which is the same thickness as the heat sink.

The fan needs to be reversed from the original mounting so it blows across the heat sink (and then across the print area) rather than sucking air from the heat si