On the invoke-diff-cmd branch: Tidy code.

* subversion/libsvn_client/diff.c
  (set_up_diff_cmd_and_options): Tidy code.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/invoke-diff-cmd-feature@1484785 13f79535-47bb-0310-9956-ffa450edef68