[fluxus] turtle enhancements commit

[Dave Griffiths]

hi all,

more in my series of random tweaks with no clear overarching direction
(there is a master plan, honest, somewhere).

(turtle-attach object) : attaches the turtle to an existing primitive for
recalculating it's points (turtle-vert) writes into the vertex position
for the current index
(turtle-skip count) : when attached to a primitive, this tells the turtle
to skip points - can be negative to go backwards. the indexing wraps

the first addition means we can deform the same primitive every frame
which speeds up the procedural turtle modelling
(http://www.pawfal.org/index.php?page=ProceduralTurtleModelling) from
around 12fps to 40fps

the second allows us to skip around topology in a way that should make
complex modelling operations possible with the turtle, like extruding a
shape with the same turtle-move, turtle-turn interface (i think)

cheers,

dave