Description:
------------
Regardless of how many file descriptors were sent with socket_sendmsg(), 
socket_recvmsg() always receives fd/0 as the very first descriptor (even if it 
wasn't sent at all) and then maximum two descriptors that were really sent.

Test script sends one descriptor $fd, but receives two, as described 
above. If we add more descriptors to send (let's say 5, and change third argument 
of socket_cmsg_space() to 5), only first two will be actually received, and extra 
fd/0 will precede them.

I know these functions are still experimental, but they are like a manna from 
heaven many backend php-developers were seeking.

Test script:
---------------
https://gist.github.com/5lava/5993637

Similar PHP test https://github.com/cataphract/php-src/blob/sendrecvmsg/ext/sockets/tests/socket_cmsg_rights.phpt taken from here: https://wiki.php.net/rfc/sendrecvmsg

Expected result:
----------------
One new file descriptors should be added after socket_recvmsg() call.

Actual result:
--------------
Two new file descriptors added.
First is always referencing fd/0, and 2nd is the one which was actually sent.

File descriptors before socket_recvmsg() call:

0 -> /etc/passwd <--- reopened fd/0
1 -> /dev/pts/3 <--- stdout
2 -> /dev/pts/3 <--- stderr
3 -> socket:[5819664] <--- $send_s
4 -> socket:[5819665] <--- $recv_s
5 -> /etc/group <--- $fd - the one we want to send
6 -> pipe:[5819666] <--- passthru() pipe

File descriptors after socket_recvmsg() call:

0 -> /etc/passwd <--- reopened fd/0
1 -> /dev/pts/3 <--- stdout
2 -> /dev/pts/3 <--- stderr
3 -> socket:[5819664] <--- $send_s
4 -> socket:[5819665] <--- $recv_s
5 -> /etc/group <--- $fd - the one we sent
6 -> /etc/passwd <--- always the same as fd/0 - shouldn't be here at all
7 -> /etc/group <--- that's the only one we expected to receive
6 -> pipe:[5819666] <--- passthru() pipe

$data contains two Resources:
Array ( ... [control] => [0] => [data] => Array (
                            [0] => Resource id #10
                            [1] => Resource id #11 ) ... )