[R] line endings in lattice plots: square vs. round

[John Bullock]

I would like to use llines() to draw lines with 
square endings in lattice plots.  But the default 
behavior seems to be to draw lines with round 
endings.  How can I change this?

I'm looking for a parameter like par('lend') or 
get.gpar('lineend'), but trellis.par.get() doesn't 
seem to have anything analogous.

I searched the archives but saw nothing on this. 
I'm running R 2.3.1 with lattice 0.13.

Thank you,
--John