wrapper does not save cpu time on legacy checkpointing

[yoyo]

The wrapper does not store cpu time in its checkpoint.txt file, if the legacy application writes its checkpoint file. To solve it I reverted method send_status_message() to its old version and in the main while (1) loop I added the following:

    poll_boinc_messages(task);
    send_status_message(task, frac_done);
    // begin yoyo
    if (task.has_checkpointed()) {
      write_checkpoint(i, cpu + task.cpu_time());
    }
    // end yoyo
    boinc_sleep(POLL_PERIOD);

[davea]

(In [16645]) - manager: clamp percentages at [0,100] in prefs dialog

fixes #794

• wrapper: if app checkpoints, write CPU time to checkpoint file

fixes #792 (I hope)