Finally, move FSFS stats logic into FSFS.  This introduces the new FSFS
private API header.

* subversion/include/private/svn_fs_fs_private.h
  (): New file describing the FSFS private API.  The content has been
      taken from the former stats-cmd.c.

* subversion/libsvn_fs_fs/stats.c
  (): New file implementing svn_fs_fs__get_stats.  All code has been
      taken from the former stats-cmd.c. 
  (svn_fs_fs__get_stats): No longer static.

* subversion/svnfsfs/stats-cmd.c
  (): Remove the statistics collection logic and data structures.
      Remove #includes of FSFS-internal headers; use the new 
      svn_fs_fs_private.h instead.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1632776 13f79535-47bb-0310-9956-ffa450edef68