Fix selection bug for Control Points.

A recent selection model change interfered with the ability to edit
the Y-axis of control points.

Timeline/Control_Point.C

@@ -112,7 +112,8 @@ Control_Point::handle ( int m )
         {
             sequence()->sort();
 
-            if ( selected() )
+            if ( nselected() > 1 )
+                // only allow horizontal movement when part of a selection...
                 break;
 
             int Y = Fl::event_y() - parent()->y();

Timeline/Sequence_Widget.H

@@ -163,6 +163,8 @@ public:
     virtual Sequence_Widget *clone ( void ) const = 0;
 
     bool selected ( void ) const;
+    int nselected ( void ) const
+        { return _selection.size(); }
     void select ( void );
     void deselect ( void );
     void remove ( void );