Issue #2220: propdel returns success on deleting a non-existent prop. * subversion/libsvn_wc/props.c (svn_wc_prop_set2): Modified with check to see if property already exists. Check done only if skip_checks is not TRUE. * subversion/clients/cmdline/propdel-cmd.c (svn_cl__propdel): Modified to always pass TRUE for the skip_checks parameter of svn_client_propset2(). * subversion/tests/clients/cmdline/prop_tests.py (remove_nonexistent_prop): Added function to test for error on removal of non-existent property. * subversion/tests/clients/cmdline/prop_tests.py (test_list): Added function with Skip().