Oops, now kira_draw needs to ensure we really have something to draw!

OK, toss those extra 'break's.

Add "kira tree" support -- tree arcs, with crosswise tick-marks
at center-of-mass points.  Tickmarks lie in screen plane, with
length of <tickscale> times true separation.

Re-extract whenever kira_set changes something.
Add particle tracking.
Compute ring sizes correctly, and draw rounder rings.

Add ring markers for non-isolated stars.  Not finished yet, but seems usable.
No GUI yet, but new commands:
   kiractl nodes  {on|off|roots}
   kiractl rings  {on|off|roots}
   kiractl ringsize {sep|semi}   (ring size from curr. separation or semimajor axis)
   kiractl scale  <scalefactor>
   kiractl span   <minpixels> <maxpixels>   (allowed range of ring radii)

Change encoding of nclump: n for leaves, -n for center-of-mass nodes,
   so colormap can make them distinguishable.

Bug: after kiractl command, must change timestep before it takes effect.
Bug: ring markers aren't colored yet for some reason.

Recode to be speedier (use recursion) and to provide more information to partiview:
	[0] worldline index (= kira index for singles, - and unique for others)
	[1] mass
	[2] number of stars (leaf nodes) in clump
		+ 100 if this is a member of an unperturbed binary
	[3] top-level name (small integer, = worldline index for single stars)
	[4] tree address in clump (0=single, 1=root, children of <i> are <2i>,<2i+1>)

Glue code to read starlab (kira) files and interpolate particle positions
into partiview internal form.