'svnadmin info': disable the public APIs for 1.8.x, by making them conditional
on an undefined preprocessor symbol.

* subversion/include/svn_fs.h
  (svn_fs_info_format, svn_fs_info_config_files, svn_fs_info_t,
   svn_fs_info, svn_fs_info_dup, SVN_FS_FSFS_INFO_SHARDED,
   SVN_FS_FSFS_INFO_REP_CACHE_PATH, SVN_FS_FSFS_INFO_MIN_UNPACKED_REV): 
    As above.

* subversion/include/svn_repos.h
  (svn_repos_capabilities, svn_repos_info_format):
    As above.

* subversion/libsvn_fs/fs-loader.c
  (svn_fs_info_format, svn_fs_info_config_files, svn_fs_info, svn_fs_info_dup):
    As above.

* subversion/libsvn_repos/repos.c
  (svn_repos_capabilities, svn_repos_info_format): As above.
* subversion/tests/libsvn_fs/fs-test.c
  (test_fs_info_format): As above.
  (test_funcs): As above.

* subversion/tests/libsvn_repos/repos-test.c
  (test_repos_info): As above.
  (test_funcs): As above.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1466597 13f79535-47bb-0310-9956-ffa450edef68