Description:
------------
The fourth (last) argument described on the socket_send function (flags) does not describe the correct set of constants used to get the described effect.  I get a message stating that any of the MSG_ constants are undefined when I attempt to use this function.

Reproduce code:
---------------
$socket = socket_create (AF_INET, SOCK_STREAM, SOL_TCP);
socket_bind ($socket, 'localhost', '54321');
socket_set_block($socket);
socket_listen ($socket);
	
while ($conn = socket_accept ($socket)) {
  socket_send ($conn, "ABCD", 4, MSG_EOF); // MSG_EOF not defined
  socket_close ($conn);
}

socket_close ($socket);

Expected result:
----------------
The expected result is that all four of the MSG_ constants are defined as documented.

Actual result:
--------------
The actual result is that the constants are undefined and the data is never sent over the socket.