Description:
------------
It's not possible to get a list of available vars.

Test script:
---------------
shm_put_var($shm, 123, 'one');
ahm_put_var($shm, 456, 'two');
var_dump(shm_list_vars($shm));

Expected result:
----------------
array(2) {
  [0]=>
  int(123)
  [1]=>
  int(456)
}
*or*
array(2) {
  [123]=>
  string(3)"one"
  [456]=>
  string(3)"two"
}

Actual result:
--------------
PHP Fatal error:  Call to undefined function shm_list_vars() in ...