Find a call out scheduled to be called either by function name or by
handle.
If the argument is a string, then the first call out due to be executed
for function 'func' is found, and the time left in seconds is returned.
If no call out is found, then return -1.
If the argument is an integer, then the call out with handle 'handle'
is found, and the time left in seconds is returned. If no call out is
found, then return -1.
This will find call outs scheduled by call_out() or call_out_walltime().
If the time remaining is fractional, then the result will be an integer,
the value of which will be floored.
Example:
int handle = call_out("func", 10);
printf("Remaining time: %O\n", find_call_out(handle));
// Remaining time: 10
int handle = call_out("func", 10.75);
printf("Remaining time: %O\n", find_call_out(handle));
// Remaining time: 10
This efun will only find call outs initiated by this_object().