On the fsfs-format7 branch:  Use a 30..40% tighter index representation.
Techniques used are delta storage and run ĺength encoding.  More tuning
in future commits.

* subversion/libsvn_fs_fs/index.c
  (l2p_page_entry_t): new aux data structure
  (encode_int,
   rle_array,
   compare_l2p_entries_by_offset,
   encode_l2p_page): new encoding utilities
  (encode_uint): 
  (svn_fs_fs__l2p_index_create): rle the page table; tighter page encoding
  (expand_rle): new decoding utility
  (get_l2p_header_body): decompress page table
  (get_l2p_page): expand l2p page
  (svn_fs_fs__p2l_index_create): deltify sub-item info;
                                 pack type & sub-item count in 1 number
  (read_entry,
   get_p2l_page): undeltify sub-item info

* subversion/libsvn_fs_fs/fs_fs.c
  (write_revision_zero): update index file templates

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1469541 13f79535-47bb-0310-9956-ffa450edef68