Changes to seeking and scrubbing from Paul Licameli.

These are mostly under an EXPERIMENTAL_ #ifdef.  Also has a change for the prompt string for preferences so the displayed keybinding is adjusted when in multitool mode.

src/TrackPanel.h

@@ -310,6 +310,10 @@ class AUDACITY_DLL_API TrackPanel:public wxPanel {
    // AS: Selection handling
    virtual void HandleSelect(wxMouseEvent & event);
    virtual void SelectionHandleDrag(wxMouseEvent &event, Track *pTrack);
+   void StartOrJumpPlayback(wxMouseEvent &event);
+#ifdef EXPERIMENTAL_SCRUBBING
+   void StartScrubbing(double position);
+#endif
    virtual void SelectionHandleClick(wxMouseEvent &event,
                                      Track* pTrack, wxRect r);
    virtual void StartSelection (int mouseXCoordinate, int trackLeftEdge);
@@ -317,6 +321,12 @@ class AUDACITY_DLL_API TrackPanel:public wxPanel {
                         Track *pTrack);
    virtual void UpdateSelectionDisplay();
 
+   // Handle small cursor and play head movements
+   void SeekLeftOrRight
+      (bool left, bool shift, bool ctrl, bool keyup,
+      int snapToTime, bool mayAccelerateQuiet, bool mayAccelerateAudio,
+      double quietSeekStepPositive, double audioSeekStepPositive);
+
 #ifdef EXPERIMENTAL_SPECTRAL_EDITING
    void StartSnappingFreqSelection (WaveTrack *pTrack);
    void MoveSnappingFreqSelection (int mouseYCoordinate,
@@ -688,6 +698,9 @@ protected:
       SBBottom, SBTop, SBCenter, SBWidth,
 #endif
    };
+   SelectionBoundary ChooseTimeBoundary
+      (double selend, bool onlyWithinSnapDistance,
+       wxInt64 *pPixelDist = NULL, double *pPinValue = NULL) const;
    SelectionBoundary ChooseBoundary
       (wxMouseEvent & event, const Track *pTrack,
        const wxRect &rect,
@@ -739,6 +752,12 @@ protected:
    int mMoveUpThreshold;
    int mMoveDownThreshold;
 
+#ifdef EXPERIMENTAL_SCRUBBING
+   bool mScrubbing;
+   wxLongLong mLastScrubTime; // milliseconds
+   double mLastScrubPosition;
+#endif
+
    wxCursor *mArrowCursor;
    wxCursor *mPencilCursor;
    wxCursor *mSelectCursor;