Added lab4ut parameter
Added experimental plot.phylo.R, which contains  several improvements over the current ape version:
* lab4ut now works also for fan and radial
* open.angle also works also for radial
* phylogram.plot is faster for very large trees (10000s taxa)
* tip.labels seem more often inside the margins (label.offset and cex)
* lab4ut="horizontal" has less empty space