comma aren't allowed in perm strings

If there is a comma in the perm string, it's displayed on the permission page but user_access always return false.

e.g.

define('MY_PERM_STRING', 'string with, comma');
// hook perm
function mymodule_perm() {
  return array(MY_PERM_STRING);
}

// then, this function always return false, even if the permission is checked on admin/user/permissions
drupal_set_message('user_access(MY_PERM_STRING) returns ' .(user_access(MY_PERM_STRING)?'OK':'KO'));