Bugfix: Fix problems with unrooted trees.
Bugfix: Fix problems with unrooted trees.

Unrooted trees have 3 nodes on its root, but they are not polytomies.
Hence should not be treated as so.

danstaines/ensembl-compara,Ensembl/ensembl-compara,danstaines/ensembl-compara,Ensembl/ensembl-compara,danstaines/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,danstaines/ensembl-compara,danstaines/ensembl-compara