When creating a gene with a canonical transcript, allow to add the internal ID of the transcript instead of the transcript itself.  The canonical_transcript() method will then lazy load the transcript.
When creating a gene with a canonical transcript, allow to add the
internal ID of the transcript instead of the transcript itself.  The
canonical_transcript() method will then lazy load the transcript.

This speeds up the gene adaptor code.

The old semantics is maintained.

at7/ensembl,james-monkeyshines/ensembl,muffato/ensembl,Ensembl/ensembl,mjg17/ensembl,at7/ensembl,muffato/ensembl,mjg17/ensembl,at7/ensembl,mjg17/ensembl,willmclaren/ensembl,Ensembl/ensembl,danstaines/ensembl,at7/ensembl,mjg17/ensembl,willmclaren/ensembl,muffato/ensembl,muffato/ensembl,james-monkeyshines/ensembl,james-monkeyshines/ensembl,danstaines/ensembl,Ensembl/ensembl,Ensembl/ensembl,james-monkeyshines/ensembl,danstaines/ensembl