Get rid of ambigiously named variables in checkout_dir().

* subversion/libsvn_ra_serf/commit.c
  (commit_dir): s/p_dir/c_dir/ as in current dir, and s/parent/c_dir_parent/


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1512209 13f79535-47bb-0310-9956-ffa450edef68