reassignment, internals, implementing time correction, but -- ...

... it does not yet interact correctly with caching, so results may be
slightly wrong if you scroll the view by less than a screen.

src/prefs/SpectrogramSettings.h

@@ -156,9 +156,7 @@ public:
    mutable float         *window;
 
    // Two other windows for computing reassigned spectrogram
-#if 0
    mutable float         *tWindow; // Window times time parameter
-#endif
    mutable float         *dWindow; // Derivative of window
 
 #endif