SFD derived from SVG tests "remove overlap" problems

After "select all" and then "Element / Overlap > / Remove Overlap"
several glyphs show wrongly filled-in areas.  GIDs 5, 6, 7, 8, 9,
12, 14, 15, and 18 show ills.

For instance, GID 5 has spline segments not removed, in both the
foreground upper-left and lower-right corners.  GID 6 is basicly
the same shape but enlarged, and shows the same effects - two areas
filled in and outline missing around the third area.

GID 9 has a new gap in the upper-left corner.

GID 14 is missing more than one original line segment.

GID 7 has some strange outline direction confusion causing the
entire shape to be black-filled.  This glyph demonstrates nested
inner regions.

I'm not sure what GIDs 12 and 15 are showing, perhaps spline
direction problems?  That some of the same glyphs elements are used
in both, but then also used in GID 13 with no problem, may help
investigation.
Merge pull request #4 from tshinnic/master

SFD derived from SVG tests "remove overlap" problems