added big_table() - calls alternative version of prepare method to avoid loading all of (e.g. dna table) into memory
added big_table() - calls alternative version of prepare method
to avoid loading all of (e.g. dna table) into memory

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