Fixed occasional 1s slippage. Disable fcrondyn if we don't have gettimeofday() (or...

Fixed occasional 1s slippage. Disable fcrondyn if we don't have gettimeofday() (or it won't work anyway)
This was due to a race condition between when time_to_sleep is run and when we compute how long to sleep for, which could happen in the following second: if that happened we end up sleeping for 1s instead of not sleeping at all.  The fix was to replace time_to_sleep() by next_wake_time().