Some more debugging output
non-tree-compliant homologies have to be created in groups
Added ENSEMBL_HOMOEOLOGUES in the API
Added ENSEMBL_HOMOEOLOGUES in the API
Cleaner way of checking whether the table is empty
New "do_transactions" mode
The species tree should be stored with a transaction in the protein-tree pipeline
Added overall list of valid methods: %single_species_ml
Simpler code to write the constraint
Shorter query + new mode to get all the nodes
Merge branch 'release/75'

* release/75:
  Shorter query + new mode to get all the nodes
  Simpler code to write the constraint
  Added overall list of valid methods: %single_species_ml
  Added ENSEMBL_HOMOEOLOGUES in the API
  Added ENSEMBL_HOMOEOLOGUES in the API
  non-tree-compliant homologies have to be created in groups
  Some more debugging output
bugfix: the array must be properly dereferenced