o yule.cov() now fits the null model, and its help page has been
corrected with respect to this change.
+ o drop.tip() has a new option 'rooted' to force (or not) a tree
+ to be treated as (un)rooted.
+
BUG FIXES
o write.tree() failed with objects of class "multiPhylo".
+ o drop.tip(, subtree = TRUE) sometimes shuffled tip labels.
+
OTHER CHANGES