added method subroot added check in add_child to speed it up
added method subroot
added check in add_child to speed it up

Ensembl/ensembl-compara,etapanari/ensembl-compara,Ensembl/ensembl-compara,ckongEbi/ensembl-compara,kumarsaurabh20/ensembl-compara,dbolser-ebi/ensembl-compara,dbolser-ebi/ensembl-compara,kumarsaurabh20/ensembl-compara,ckongEbi/ensembl-compara,danstaines/ensembl-compara,dbolser-ebi/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,danstaines/ensembl-compara,danstaines/ensembl-compara,etapanari/ensembl-compara,kumarsaurabh20/ensembl-compara,ckongEbi/ensembl-compara,danstaines/ensembl-compara,etapanari/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,kumarsaurabh20/ensembl-compara,Ensembl/ensembl-compara,etapanari/ensembl-compara,Ensembl/ensembl-compara,danstaines/ensembl-compara