#83 clipdetect should exit with nonzero status if clipping is detected

[Avedis]

When using --clipdetect, the exit status should be nonzero if clipping is detected. Currerntly it returns an exit status of 0, which I would only expect if no clipping was detected (while using --clipdetect).

Alternatively, have --clipdetect and --replaygain-accurate automatically set a --scale value such that clipping does not occur. This would be preferred, but obviously more work than just having --clipdetect force lame to exit with status if clipping is detected.