Fixes a bug where an arc, ellipse, or arc-of-ellipse, being reversed in
XY plane, behaved badly in sketcher (see forum thread "Sketch: how to
handle reversed external arcs?"
http://forum.freecadweb.org/viewtopic.php?f=10&t=9130 ).
Also fixes a problem with rotated arcs (see forum thread "Rotating Arc
in Sketcher"
http://forum.freecadweb.org/viewtopic.php?f=22&t=9145#p74262 ).
This is done by adding an emulation flag to a few methods in
Part::GeomXXX, which makes the shape to pretend being non-reversed
(CCW). This causes endpoints of reversed arcs of circles lineked as
external geometry to swap, causing broken sketches sometimes.
0767cd35f8