On the thunder branch:  Make our block_read feature THUNDER-aware.
Since this is a generic reader, we can't use our cache wrapper
functions here.

* subversion/libsvn_fs_fs/cached_data.c
  (block_read): Callers need to provide the item type such that
                we may retry the cache lookup later.
  (get_node_revision_body,
   create_rep_state_body, 
   read_delta_window,
   svn_fs_fs__get_changes): Provide the extra parameter.
  (block_read): Coordinate the data access with the THUNDER registry
                and manually retry the cache-lookup.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/thunder@1586571 13f79535-47bb-0310-9956-ffa450edef68