Fix IterativeRobot/TimedRobot RobotInit(). (#633)

In C++, it's not legal to call a virtual function from within a constructor,
so the user override was never called (the base function is always called).

See https://isocpp.org/wiki/faq/strange-inheritance#calling-virtuals-from-ctors

While this is technically allowed in Java, also change Java for consistency.

wpilibc/src/main/native/cpp/TimedRobot.cpp

@@ -17,6 +17,11 @@ using namespace frc;
  * Provide an alternate "main loop" via StartCompetition().
  */
 void TimedRobot::StartCompetition() {
+  RobotInit();
+
+  // Tell the DS that the robot is ready to be enabled
+  HAL_ObserveUserProgramStarting();
+
   // Loop forever, calling the appropriate mode-dependent function
   m_startLoop = true;
   m_loop->StartPeriodic(m_period);