Printing an error should stringify structures included in the error message

[yzhernand]

I'm using Bio::DB::EUtilities to fetch linked assemblies for some input nuccore accessions. Occasionally, the server responds with an error instead of a history. The result is a warning like this printed to stderr:

--------------------- WARNING ---------------------
MSG: NCBI LinkSet error: nuccore: ARRAY(0x55fa47a7f880)

---------------------------------------------------

I traced the message back to Bio::Tools::EUtilities::Link, line 49. There, the code simply extracts the contents of the 'ERROR' key in the link set (?) and passes it to the warn method.

I added one line of code so that I could turn the arrayref into a string and see what errors I was getting:

$error = join ", ", @$error;
$self->warn("NCBI LinkSet error: $dbfrom: $error\n");

Now I can see what some of the errors were:

--------------------- WARNING ---------------------
MSG: NCBI LinkSet error: nuccore: BLOB ID IS NOT IMPLEMENTED, BLOB ID IS NOT IMPLEMENTED

I could submit a pull request with that change if that acceptable as a solution to you all.