find_call_out() - find a call out scheduled to be called next

int find_call_out( string func ):

Find  the  first  call  out due to be executed for function 'func', and
return the time left. If it is not found, then return -1.

This efun will only find call outs initiated by this_object().

call_out(3), remove_call_out(3), set_heart_beat(3)