[PATCH] remove inode.i_wait

[PATCH] remove inode.i_wait

Remove i_wait from struct inode and hash it instead.

This is a pure space-saving exercise - 12 bytes from struct
inode on x86.

NFS was using i_wait for its own purposes.  Add a wait_queue_head_t to
the fs-private inode for that.  This change has been acked by Trond.