Used new WPILIB2015 macro to mark differences with the old WPILib.

Change-Id: I9e45a22096bdb108f74f9dc341037d5f64506ff5
diff --git a/frc971/wpilib/buffered_pcm.h b/frc971/wpilib/buffered_pcm.h
index 50f86fc..e2613d7 100644
--- a/frc971/wpilib/buffered_pcm.h
+++ b/frc971/wpilib/buffered_pcm.h
@@ -29,7 +29,9 @@
 
  private:
   // WPILib declares this pure virtual and then never calls it...
+#ifdef WPILIB2015
   virtual void InitSolenoid() override {}
+#endif
 
   void Set(int number, bool value);