Added generation of gene descriptions. Previously these were done via a separate script, now they are generated as part of the post-xref-mapping phase.

New implementation uses the same precedence rules for deciding which xref description to assign to a gene as the old script.

In fetch_by_Transcript, updated a throw message so that it says which transcript_id is causing problem

generate a file of %id's and the accession names from the map files. Only process those from the list (acc_file) so lists can be made for seperate sources if wanted

Changed field separator in input file from one tab to one or more whitespace characters; makes input file formatting less error-prone.

Making mRNA xref dependent on peptide isn't needed and is actually quite confusing on the web display.

Deal with 2 different sources instead of just one - RefSeq_peptide & RefSeq_dna - since Mart needs one type per source.

Modified appropriate source_url entries as well.

fix bug that if -dumpcheck set and files not found then the script failed instead of dumping the files