Add a reinit() stub for subsystems, so that they can be reinitialized

when needed (say, to reload the configuration files).

src/Main/fgfs.cxx

@@ -26,6 +26,11 @@ FGSubsystem::init ()
 {
 }
 
+void
+FGSubsystem::reinit ()
+{
+}
+
 void
 FGSubsystem::bind ()
 {

src/Main/fgfs.hxx

@@ -148,6 +148,15 @@ public:
   virtual void init ();
 
 
+  /**
+   * Reinitialize the subsystem.
+   *
+   * <p>This method should cause the subsystem to reinitialize itself,
+   * and (normally) to reload any configuration files.</p>
+   */
+  virtual void reinit ();
+
+
   /**
    * Acquire the subsystem's property bindings.
    *