Did you check the root directory for a file named "this_system_is_vulnerable"? I just tested this on a mid-2015 MBP running 10.10.4 and found that file in the root directory. :(
$ ls -al /
(etc)
-rw-r--r-- 1 root wheel 0 Aug 6 06:46 this_system_is_vulnerable
and b) the patch works: I ran the patch, deleted the test file, rebooted and the file is no longer able to be written.