On the fsfs-format7 branch: complete the index implemenation, in particular
fix packing problems and add transaction support.  Also, properly document
all of it.

* subversion/libsvn_fs_fs/index.h
  (SVN_FS_FS__ITEM_INDEX_UNUSED,
   SVN_FS_FS__ITEM_INDEX_CHANGES,
   SVN_FS_FS__ITEM_INDEX_ROOT_NODE,
   SVN_FS_FS__ITEM_INDEX_FIRST_USER,
   SVN_FS_FS__ITEM_TYPE_UNUSED,
   SVN_FS_FS__ITEM_TYPE_REP,
   SVN_FS_FS__ITEM_TYPE_NODEREV,
   SVN_FS_FS__ITEM_TYPE_CHANGES): define new constants
  (svn_fs_fs__p2l_entry_t,
   svn_fs_fs__l2p_proto_index_open,
   svn_fs_fs__l2p_proto_index_add_revision,
   svn_fs_fs__l2p_proto_index_add_entry,
   svn_fs_fs__p2l_proto_index_open,
   svn_fs_fs__p2l_proto_index_add_entry,
   svn_fs_fs__p2l_index_lookup): document
  (svn_fs_fs__l2p_index_create,
   svn_fs_fs__p2l_index_create): document; explicitly specify input and
   output file names which is useful during rev file packing
  (svn_fs_fs__l2p_index_lookup): drop; replaced by svn_fs_fs__item_offset
  (svn_fs_fs__item_offset): document; add support for data still in txns

* subversion/libsvn_fs_fs/index.c
  (ENCODED_INT_LENGTH,
   l2_index_page_table_entry,
   l2p_index_header_t,
   l2p_index_page_t,
   l2_proto_index_entry_t,
   p2l_index_header_t,
   encode_uint,
   get_l2p_header,
   get_p2l_header,
   read_entry): document
  (svn_fs_fs__l2p_proto_index_open,
   svn_fs_fs__p2l_proto_index_open): update
  (svn_fs_fs__l2p_proto_index_add_entry): document; map offset '-1' to uint64
  (svn_fs_fs__l2p_index_create): update, fix and document
  (read_number): document and fix 
  (get_l2p_page): document; fix offset table reading
  (svn_fs_fs__l2p_index_lookup): document; no duplicate offset correction
  (l2p_proto_index_lookup): new internal utility function
  (svn_fs_fs__p2l_index_create): update; fix page boundary detection
  (get_p2l_page): document; fix page end detection
  (svn_fs_fs__item_offset): update



git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1434413 13f79535-47bb-0310-9956-ffa450edef68