In the diff output handling: handle copyfrom information as intended years ago.

* subversion/libsvn_client/diff.c
  (includes): Add svn_subr_private.h.
  (diff_cmd_baton): Add two variables.
  (diff_file_added): When suppressing copies, rebase the input to produce
    the right output for plain adds.

  (svn_client_diff6,
   svn_client_diff_peg6):
     Set value in baton.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1444545 13f79535-47bb-0310-9956-ffa450edef68