Friendlier x/y belt pulley for Mendel/Huxley

A slightly more printer friendly version of the small x and y belt pulleys found on the Reprappro Huxley and Mendel (and probably other printers that use a belt of the same type).

I was having issues printing the .stl that reprappro provided because Slic3r was trying to get my printer to make two round shells and then extrude tiny, lonely drops to make the teeth.
(https://github.com/reprappro/Mendel/blob/master/Print-mendel/Individual-STLs/pulley-2off.stl)

I made the teeth on the gear m