An undefined class constant caused a fatal error when running the
example - "Fatal error: Undefined class constant 'NOCLEAR' in
asyncsrv.php on line..."
Class name should start with a Capital letter.  This is the only place
where it is with a lower case.  In all other places in the examples, it
is with a capital Z, for example

$zmsg = new Zmsg($client);
Merge pull request #435 from karnaf/master

Fatal Error when running this example