Next step fixing 'svnfsfs stats' scalability for f6: A bit of refactoring.

Factor out the actual revision parsing sequence for physically addressed
revisions into a common function.

* subversion/libsvn_fs_fs/stats.c
  (read_phys_revision): New function. Logic taken from ...
  (read_phys_pack_file,
   read_phys_revision_file): ... here. Call the new function.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1639322 13f79535-47bb-0310-9956-ffa450edef68