Description:
------------
If I create a Shared memory segment using shm_attach with one user, and set it as readable by all users, but only writable by the owner, then other users cannot open the segment via shm_attach, they get permission denied errors.

I would guess this is maybe because shm_attach can't open a segment as read-only, and always tried to open it as rw?

Reproduce code:
---------------
run as someuser1:

<?php
   $f = ftok('somefile', 'I');
   $sh = shm_attach($f, 1024000, 0644);
?>

works if its not already created by another user...


run as someuser2:

<?php
   $f = ftok('somefile', 'I');
   $sh = shm_attach($f);
?>



Expected result:
----------------
what I would expect is that since I created it as 0644, other users should be able to access it via read-only mode (which I can do if I open it using shmop_open with the read-only flag instead).

Actual result:
--------------
second user gets "Permission Denied" php warning messages.

once again, I think this is mearly a result of shm_attach not actually ever opening an shm as read-only, always read-write... but I might be mistaken. 


Thanks.