Use comet magnitude model for large eccentricities

[Bill-Gray]

At present, Find_Orb uses the "standard" asteroid H/G magnitude model unless an object has a comet designation. In that case, it uses a comet magnitude model.

That decision really ought to involve looking at the orbit. If the object is in a near-parabolic orbit, the comet magnitude model should be used. (And if it's in orbit around the earth, an artsat magnitude model should be used... but that's another issue (q. v.).)