incorrect bounds for Bezier segments

[fryguybob]

(Imported from http://code.google.com/p/diagrams/issues/detail?id=23. Original issue from byor...@gmail.com on April 18, 2011, 11:10:59 PM UTC)

See attached file which exhibits the problem; the square ought to be next to the curvy triangular path, but intersects it instead.

Not sure whether it's a bug in lib or core.

[fryguybob]

(Imported. Original comment by byor...@gmail.com on April 19, 2011, 02:12:32 PM UTC)

The problem isn't really with trails or composition; the bounding function for Bezier segments itself is wrong.

[fryguybob]

(Imported. Original comment by byor...@gmail.com on April 19, 2011, 02:26:56 PM UTC)

Doh! The bug was really dumb: I began by writing down the wrong formula for Bezier segments in a comment (forgot the factors of 3 in the (1-t)^2 t and (1-t) t^2 terms), then proceeded to "correctly" work out the derivative when projecting against a given vector, etc...