[R] Lattice: Add abline to Single Value qqmath() Plot

[Rich Shepard]

   The data are not normally distributed when untransformed and I'm trying
various transformations to see if any would be appropriate to use. The
lattice book (fig. 3.10) shows a 2-sample Q-Q plot with an abline but the
code for the figure does not include the line.

   I'd appreciate a pointer to a reference on how to add an abline to a
one-sample qqmath() plot in lattice.

Rich