Stylization: Retrieve the original elliptical arc definition

[danstoica]

Currently there is no way to retrieve the original arc definition from SE_LineBuffer class but only the arc in the tessellated form.

Sometimes the client needs to distinguish between circular arcs and ellitical arcs or it needs to reconstruct the geometry. Although possible to use the tessellated arc to accomplish this, it is both inconvenient and error prone from accuracy standpoint.

The solution is to add a public method to SE_LineBuffer which returns the arc definition. This will complement xf_buffer() method.

[waltweltonlair]

Submitted fix from Dan (reviewed by me) - r4962