Warn users of the buggy behaviour of sem_get() with non-PHP semaphores.

Fixes doc bug #66270 (sem_get() expects an already created pack of semaphores
to have 3 of them).


git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@332354 c90b9560-bf6c-de11-be94-00142212c4b1