Added feature to sort members in alignments.
Added feature to sort members in alignments.

This is to assure that we have always the same order when dumping and
re-mapping an alignment. Used by ExaML checkpoints.

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