Speed up fixture loading by bulk insert

[JorisBenschop]

I noticed that loading many fixtures is fairly inefficient, in that it tries an update and then an insert for each record. I would propose an additional option to the command line (—bulk-insert) that only runs the insert queries, but also detects if subsequent items in the fixtures are from the same model, so they may be inserted using bulk_insert. If there is genuine interest in this feature i will develop it and submit. I have this running in my own codebase already.
Please also indicate if there is no interest, and i spend my energy elsewhere =)