added cacheing to Exon->seq() call
added cacheing to Exon->seq() call

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