v1.3.9 fixed two bugs

- big bug derived from data availability for adjusting margin in
plot_tree. This follows a reorganization of the code so that margin
adustment can occur on other tree plot methods (right now just
"treeonly")
- Fixed warning from plot_tree() about data missing. This appears to be
needless warning that would scare/distract users. Solved with
na.rm=TRUE param in many geom_*() functions in plot-methods.R