Add RemoveRepeatedPoints

[peterstace]

• Add new methods RemoveRepeatedPoints() T to MultiPoint, LineString, MultiLineString, Polygon, MultiPolygon, GeometryCollection and Geometry. T should be the type that the method is implemented on.
• We don't need to add it to Point because Points cannot have repeated points.
• The method should remove any repeated points in rings (for Polygon/MultiPolygon)
• The method should remove any repeated points in linestrings (for LineString/MultiLineString)
• The method should removed any duplicated points in MultiPoint (even if they're not adjacent).
• It should operate recursively on the Geometry and GeometryCollection types.

[peterstace]

I've got a WIP for this in remove_repeated_points, but I'm running into significant problems with the GEOS comparison tests. I'll park this for now and come back later.