add not_dna flag to avoid storing sequence if it is not a dna database
add not_dna flag to avoid storing sequence if it is not a dna database

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