making LoadFile split a file up on semi-colons

This makes LoadFile() more suitable for doing bulk loads, sending semicolon separated queries. Feedback welcome--I can't think of any problems with it, but I only tested with jackc/pgx and go-cq/cq. Bleh, just realized semi-colons in comments that are in the middle of queries might screw things up, but that doesn't seem like a huge deal. I can fix it if you like the idea of this PR.