[PATCH] md: Misc little raid fixes

[PATCH] md: Misc little raid fixes

Roughly in order of patch:

1/ xor.h is never needed in md.c
2/ set sb_loaded when we 'sync' mddev to rdev as well as when we load
   sb into rdev from disk.
2/ due to lifetime changes, active count can be 2 when we stop array
3/ due to lifetime changes, we need to explicitly clear the ->pers when we
   stop an array
4/ autostart can only work for 0.90.0 superblocks.
   None others would be silly enough to store device numbers for
   all devices in the superblock...
5/ we had lost the setting of 'sb' when auto-starting an array.
6/ Code currently calls export_rdev(start_rdev) when
   IS_ERR(start_rdev), which causes an oops.
7/ /proc/mdstat contents error:
       code does not take into account that delayed
       resyncs can wait with curr_resync = 1 or 2.
8/ There is a premature "return NOTIFY_DONE", that possibly was in
   for debugging once...