Grobs that are their own ancestors.

[mike]

I've now gone on a quest for parental loops in the source, and I've found some:

chord-repetition.ly
chord-tremolo-articulations.ly
dynamics-alignment-breaker.ly
dynamics-alignment-no-line.ly
dynamics-glyphs.ly
dynamics-line.ly
dynamics-rest-positioning.ly
dynamics-text-right-padding.ly
dynamics-text-spanner-abs-dynamic.ly

After this I stopped checking, but in all of these, the DynamicLineSpanner is 
its own parent if you trace back its ancestry.  The culprit is line 179 of 
dynamic-align-engraver - if anyone has any intuition as to why this is the 
case, lemme know!  Otherwise, I'll be able to look into it next week.

Then, in context-die-staff.ly, in fixup_refpoint, a grob is passed a null 
pointer as its parent (the variable newparent).  Any ideas as to where this 
error may be coming from?

Cheers,
MS