Revision 1464993

'svnadmin info': sketch the public API.

Declare the new APIs:
* subversion/include/svn_fs.h
  (svn_fs_info, svn_fs_info_t, svn_fs_info_dup): New.

* subversion/include/svn_repos.h
  (svn_repos_info, svn_repos_info_t, svn_repos_info_dup): New.
  (svn_repos_capabilities): New.

And provide "Not implemented" definitions:

* subversion/libsvn_fs/fs-loader.c
  (svn_fs_info, svn_fs_info_dup): Dummy implementations.

* subversion/libsvn_repos/repos.c
  (svn_repos_info, svn_repos_info_dup): Dummy implementations.
  (svn_repos_capabilities): Dummy implementation.