This changeset:

1. Implements hlist_add_after
2. uses prefetch in hlist_for_each, using a trick that ends up being
   equivalent to having the prefetch instruction in the first block
   of the hlist_for_each for block, the compiler optimizes the second
   "test" away, as its result is constant
3. implements hlist_for_each_entry and hlist_for_each_entry safe,
   using a struct hlist_node as iterator to avoid the extra branches a
   similar implementation to list_for_each_entry would have if used
   a typed iterator, but while avoiding having to have the explicit
   hlist_entry as in hlist_for_each.

4. Converts the hlist_for_each users that had explicit prefetches, i.e.
   removed the explicit prefetch

5. fix a harmless list_entry use in a hlist_for_each in inode.c