Contrasts-based calculations of BM likelihoods.
Drop srcref attribute when rewriting default, and test rewriting works
Generating function for simulating character histories
Bug fix for contrasts calculation with intermediates
Handed alpha=0 case gracefully for VCV OU calculation.
Fix bug in time calculation that did not work on non-cladewise tree.

This may affect calculations under split models.
Tree rescaling code
Bugfix in EB pruning calculations (with R backend only)
OU via contrasts and rescaling
Simplify OU rescaling code.
OU models now have "with.optimum" option.

Also much more extensive tests for OU cases.

The "with.optimum" argument represents a major interface change
for the OU models, but is important.  The default will be to fit
models like the fitContinuous models, where there is no optimum
parameter (and it will be fixed at something like its ML state).

For "pruning" based models only, the optimum can be treated as a
parameter, which is a slightly different version of OU.  It remains
unclear to me exactly how these are related.
Documentation and NOTE fixes from R CMD check