Documentation fixes to the 1.9 svn_diff API.  No functional change.
Documentation fixes to the 1.9 svn_diff API.  No functional change.

* subversion/include/svn_diff.h
  (svn_diff_output2,
   svn_diff_file_output_unified4): Document cancelation functionality.
  (svn_diff_file_output_unified3): Fix reference to bumped API.
  (svn_diff_file_output_merge3: Document cancelation functionality.
  (svn_diff_output_binary): Same. Fix a typo.
  (svn_diff_mem_string_output_unified3,
   svn_diff_mem_string_output_merge3): Document cancelation functionality.

git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1670337 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion