On the fsfs-format7 branch:  Introduce a container data structure
for node revisions.

* subversion/libsvn_fs_fs/noderevs.h
  (svn_fs_fs__noderevs_t): declare container data type
  (svn_fs_fs__noderevs_create,
   svn_fs_fs__noderevs_add,
   svn_fs_fs__noderevs_estimate_size,
   svn_fs_fs__noderevs_get,
   svn_fs_fs__write_noderevs_container,
   svn_fs_fs__read_noderevs_container): declare container API

* subversion/libsvn_fs_fs/noderevs.c
  (NODEREV_KIND_MASK,
   NODEREV_HAS_MINFO,
   NODEREV_HAS_COPYFROM,
   NODEREV_HAS_COPYROOT,
   NODEREV_HAS_CPATH): define various encoding flags & fields
  (binary_id_t,
   struct binary_noderev_t,
   svn_fs_fs__noderevs_t): define data types
  (store_id,
   store_representation,
   get_id,
   get_representation,
   create_rep_stream,
   write_reps,
   read_reps): utility functions
  (svn_fs_fs__noderevs_create,
   svn_fs_fs__noderevs_add,
   svn_fs_fs__noderevs_estimate_size,
   svn_fs_fs__noderevs_get,
   svn_fs_fs__write_noderevs_container,
   svn_fs_fs__read_noderevs_container): implement container API

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1467454 13f79535-47bb-0310-9956-ffa450edef68