Librarian does not check upper limit on filesize

We currently store the file size of Librarian files in the database using a normal PostgreSQL integer. This does not support files larger than 2GB. We should switch this column to bigint to support DVD images or huge source packages, such as discussed in https://answers.edge.launchpad.net/soyuz/+question/93944 where a person was uploading a 3gb source package and was not receiving any upload error even though the file uploaded successfully.

The following log shows the exception while processing the upload:
http://pastebin.ubuntu.com/345209/

and the actual traceback is:

http://launchpadlibrarian.net/36972844/mfPJuIGJVq6E7KhT95s1WLCuKJn.txt

which shows that "DataError: integer out of range" is raised because we're using PostgreSQL's (signed) 4byte integer to store the file size (max. 2147483648 bytes).