Fix issue 4111, update under add with not-present parent.

* subversion/libsvn_wc/node.c
  (svn_wc__node_get_base): Ignore not-present nodes.

* subversion/tests/cmdline/update_tests.py
  (update_child_below_add): Tweak status, remove XFAIL.

* subversion/tests/libsvn_wc/op-depth-test.c
  (test_funcs): Mark update_child_under_add PASS.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1448784 13f79535-47bb-0310-9956-ffa450edef68