Improve cancel-ability of unified diff output.
Improve cancel-ability of unified diff output.

Before this patch it was not possible to cancel the output of a file addition
or removal during 'svn diff' within the file on Windows.

* subversion/libsvn_client/diff.c
  (svn_diff__file_output_baton_t): Add cancel function.
  (output_unified_diff_range): Support cancelling.
  (output_unified_flush_hunk,
   output_unified_diff_modified): Update caller.
  (svn_diff_file_output_unified4): Set cancel function in baton.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1706366 13f79535-47bb-0310-9956-ffa450edef68

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