int find_call_out(string func)
int find_call_out(closure func)
Find the first call-out due to be executed for function <func>
in the current object resp. for the closure <func>, and return the
time left. If no call-out is found return -1.
Finding a call_out to a closure was introduced in 3.2.1@45.
call_out(E), remove_call_out(E), call_out_info(E)