Rename variable to be consistent with other tests.  No functional change.

* subversion/tests/libsvn_client/client-test.c
  (test_suggest_mergesources): s/wc_dir/wc_path/


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1558947 13f79535-47bb-0310-9956-ffa450edef68