[Bug-barcode] barcode does not encode ISBN 13

[Goulven Guillard]

Hi,

The barcode manpage claims that "ISBN numbers are encoded as EAN-13 
symbols", though it only lists ISBN 10 examples.

However, the following command :

$ barcode -e ISBN -b 1234567890123

results in the following error :

barcode: can't encode "1234567890123"

Indeed, it seems to only work when the input string is 10 digits.

Regards,

Goulven Guillard.