Improve logging of genbank parsing errors

When a genbank file contains errors then the error report is not informative. For example, a user opens a file with the following strings:
FEATURES Location/Qualifiers
source -1..12766

and he sees the error: "Error parsing location". But he is sure that the file is correct, because he has got this file from some annotating program, for example.

Maybe, it will be good to inform users more exact about the errors (e.g. "-1..12766 is an incorrect location. ..." or something like that).