On the invoke-diff-cmd branch: Improve variable names.

* subversion/libsvn_subr/io.c

  (svn_io_create_custom_diff_cmd): Improve variable names.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/invoke-diff-cmd-feature@1489166 13f79535-47bb-0310-9956-ffa450edef68