This morning's fix for elv_former_request() is causing oopses all over the
place in the IO scheduler.

Jens, remember that I did try that fix a while ago, and the same happened.

I believe it has exposed a new problem at the __make_request/attempt_front_merge
level: if attempt_front_merge() actually succeeds, the wrong request gets freed
up in elv_merged_request().

It may be best to back this change out until it can be fixed up for real.