On the fsfs-format7 branch: Add packing support to format7.

* subversion/libsvn_fs_fs/pack.c
  (copy_indexes): new utility copying info from non-packed to packed indexes
  (pack_rev_shard): depending on the repo format, either write indexes or
   manifest files
  (pack_shard): update caller

* subversion/tests/libsvn_fs_fs/fs-pack-test.c
  (pack_filesystem): check for the right files to be present depending on
   repository format

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1434462 13f79535-47bb-0310-9956-ffa450edef68