On the log-addressing branch:  Extend verification code to check
for index consistency, i.e. log-to-phys must match phys-to-log 1:1.

To do this, we need two extra functions in the index API that
basically tell us the size of the index.

* subversion/libsvn_fs_fs/index.h
  (svn_fs_fs__l2p_get_max_ids,
   svn_fs_fs__p2l_get_max_offset): declare new private API

* subversion/libsvn_fs_fs/index.c
  (get_l2p_header): caching wrapper around get_l2p_header_body as
                    the other functions won't return the full header
  (svn_fs_fs__l2p_get_max_ids): implement
  (p2l_get_max_offset_func): cache data extraction function
  (svn_fs_fs__p2l_get_max_offset): implement

* subversion/libsvn_fs_fs/verify.c
  (compare_l2p_to_p2l_index,
   compare_p2l_to_l2p_index): implement two-way index comparison
  (verify_index_consistency): new verification function
  (svn_fs_fs__verify): call the new function for log. addressed range

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/log-addressing@1512240 13f79535-47bb-0310-9956-ffa450edef68