Fix #1575:  ensure we never try to generate a diff on a binary-marked file.
Fix #1575:  ensure we never try to generate a diff on a binary-marked file.

* libsvn_client/diff.c (diff_file_changed):  if either file has a
  binary mime-type, don't attempt to generate a diff at all.  Just
  output a warning and exit early.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@847623 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion