On the fsfs-format7 branch: cache noderevs containers

* subversion/libsvn_fs_fs/fs.h
  (fs_fs_data_t.noderevs_container_cache): add cache as new member
* subversion/libsvn_fs_fs/caching.c
  (svn_fs_fs__initialize_caches): initialize the new cache for fsfs-f7

* subversion/libsvn_fs_fs/noderevs.h
  (svn_fs_fs__serialize_noderevs_container,
   svn_fs_fs__deserialize_noderevs_container): declare cache serialization /
                                               deserialization functions
* subversion/libsvn_fs_fs/noderevs.c
  (svn_fs_fs__serialize_noderevs_container,
   svn_fs_fs__deserialize_noderevs_container): implement them

* subversion/libsvn_fs_fs/cached_data.c
  (get_node_revision_body): hit the new cache, if applicable
  (block_read_changes_container): populate the new cache


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1476626 13f79535-47bb-0310-9956-ffa450edef68