From: Nick Piggin <piggin@cyberone.com.au>

This fixes a bug in deadline and AS that causes insert_here to be ignored on
blk_fs_requests. This has been causing problems with SCSI requeueing code.
It makes elevator insertion more correct as advertised wrt insert_here and
REQ_SOFTBARRIER.

It also fixes a buglet in the as_requeue code where the request wasn't being
put into the front of the list (in rare cases).