Description:
------------
Adding function to get total size of memory and to get free size of memory of the opened shm segment.

Test script:
---------------
From test script:

// test errors
var_dump(shm_stat());
var_dump(shm_stat(1));
var_dump(shm_stat(""));

// open shm segment
$key = ftok(dirname(__FILE__)."/008.phpt", 't');
$shmId = shm_attach($key, 1024);
var_dump($shmId);

// first stat call
var_dump(shm_stat($shmId));

// write data + stat
var_dump(shm_put_var($shmId, 10, '10'));
var_dump(shm_put_var($shmId, 20, '20'));
var_dump(shm_put_var($shmId, 30, '30'));
var_dump(shm_stat($shmId));

// remove data + stat
var_dump(shm_remove_var($shmId, 20));
var_dump(shm_stat($shmId));

// re-open shm segment with different size + stat
var_dump(shm_detach($shmId));
$shmId = shm_attach($key, 10240);
var_dump($shmId);
var_dump(shm_stat($shmId));

// remove shm segment + stat
var_dump(shm_remove($shmId));
var_dump(shm_stat($shmId));

echo "Done\n";

Expected result:
----------------
Warning: shm_stat() expects exactly 1 parameter, 0 given in %s on line %d
bool(false)

Warning: shm_stat() expects parameter 1 to be resource, integer given in %s on line %d
bool(false)

Warning: shm_stat() expects parameter 1 to be resource, string given in %s on line %d
bool(false)
resource(%d) of type (sysvshm)
array(2) {
  ["total"]=>
  int(1024)
  ["free"]=>
  int(%d)
}
bool(true)
bool(true)
bool(true)
array(2) {
  ["total"]=>
  int(1024)
  ["free"]=>
  int(%d)
}
bool(true)
array(2) {
  ["total"]=>
  int(1024)
  ["free"]=>
  int(%d)
}
bool(true)
resource(%d) of type (sysvshm)
array(2) {
  ["total"]=>
  int(1024)
  ["free"]=>
  int(%d)
}
bool(true)
array(2) {
  ["total"]=>
  int(1024)
  ["free"]=>
  int(%d)
}
Done