alexrj/Slic3r — pull request #722 by mesheldrake (2012-09-27 14:01:08+00:00)
Title: use remove_coinciding_points before convex_hull

Math::ConvexHull can give invalid results if it's input has duplicate points, and it only
screens for sequential duplicates. Non-sequential
duplicates resulting from flattening multiple z-level slices sometimes lead to erroneous, non-convex polygon output.

STL: http://dl.dropbox.com/u/315849/Slic3r/z-motor-mount.stl

before and after fix:

![non-convex hull on the plater, and fix](https://a248.e.akamai.net/camo.github.com/de2d26c6b212c45dc995529200b4021c0fcf7df7/687474703a2f2f7368656c6472616b652e6e65742f6261672f636f6e7665785f68756c6c5f6669782e706e67)

Affects plater display, validate, and skirt.