Add a mechanism for strip age

The getPushedAt() method in Strip allows you to determine how recently
a strip was pushed.  Since PixelPusher is asynchronous, it might sit in
the pipeline for some time, and this allows applications to determine
how long.

A value of 0 indicates that the strip has not yet been pushed since it
was last updated;  otherwise, the value is in the same timebase as
System.nanoTime().

src/com/heroicrobot/dropbit/devices/pixelpusher/CardThread.java

@@ -259,6 +259,7 @@ private int sendPacketToPusher(PixelPusher pusher) {
           } else {
             stripPacket = strip.serialize(DeviceRegistry.getOverallBrightnessScale());
           }
+          strip.setPushedAt(System.nanoTime());
           strip.markClean();
           this.packet[packetLength++] = (byte) strip.getStripNumber();
           if (fileIsOpen) {

src/com/heroicrobot/dropbit/devices/pixelpusher/Strip.java

@@ -13,6 +13,7 @@ public PixelPusher getPusher() {
     return pusher;
   }
 
+  private long pushedAt;
   private int stripNumber;
   private boolean touched;
   private double powerScale;
@@ -155,6 +156,7 @@ public long getStripIdentifier() {
   public synchronized void setPixels(Pixel[] pixels) {
     this.pixels = Arrays.copyOfRange(pixels, 0, this.pixels.length);
     this.touched = true;
+    pushedAt = 0;
     pusher.markTouched();
   }
 
@@ -171,6 +173,7 @@ public synchronized void setPixelRed(byte intensity, int position) {
       nope.printStackTrace();
     }
     this.touched = true;
+    pushedAt = 0;
     pusher.markTouched();
   }
 
@@ -187,6 +190,7 @@ public synchronized void setPixelBlue(byte intensity, int position) {
       nope.printStackTrace();
     }
     this.touched = true;
+    pushedAt = 0;
     pusher.markTouched();
   }
 
@@ -203,6 +207,7 @@ public synchronized void setPixelGreen(byte intensity, int position) {
       nope.printStackTrace();
     }
     this.touched = true;
+    pushedAt = 0;
     pusher.markTouched();
   }
 
@@ -219,6 +224,7 @@ public synchronized void setPixelOrange(byte intensity, int position) {
       nope.printStackTrace();
     }
     this.touched = true;
+    pushedAt = 0;
     pusher.markTouched();
   }
 
@@ -235,6 +241,7 @@ public synchronized void setPixelWhite(byte intensity, int position) {
       nope.printStackTrace();
     }
     this.touched = true;
+    pushedAt = 0;
     pusher.markTouched();
   }
 
@@ -251,6 +258,7 @@ public synchronized void setPixel(int color, int position) {
       nope.printStackTrace();
     }
     this.touched = true;
+    pushedAt = 0;
     pusher.markTouched();
   }
 
@@ -260,6 +268,7 @@ public synchronized void setPixel(Pixel pixel, int position) {
     else
       this.pixels[position].setColor(pixel);
     this.touched = true;
+    pushedAt = 0;
     pusher.markTouched();
   }
 
@@ -346,4 +355,12 @@ public boolean isNotIdempotent() {
   public void setNotIdempotent(boolean isNotIdempotent) {
     this.isNotIdempotent = isNotIdempotent;
   }
+
+  public long getPushedAt() {
+    return pushedAt;
+  }
+
+  public void setPushedAt(long pushedAt) {
+    this.pushedAt = pushedAt;
+  }
 }