On the fsfs-format7 branch: access index files in FFD->BLOCK_SIZE.

* subversion/libsvn_fs_fs/index.c
  (packed_number_stream_t): store block size as needed for aligned seeks
  (packed_stream_read): update; improve error message
  (packed_stream_open): add block size parameter
  (get_l2p_header,
   get_l2p_page,
   get_p2l_header,
   get_p2l_page): update callers

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1444669 13f79535-47bb-0310-9956-ffa450edef68