acet-geom-is-arc

(acet-geom-is-arc  p1  p2  p3  p4 fuz)

Verifies, whether given 4 points p1 p2 p3 p4 define a valid arc/circle;
fuz is a numerical tolerance - if NIL, tolerance 0.0 is used.

Returns T if the 4 points belong to an arc/circle, NIL otherwise