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/IterativeRobot.cpp

@@ -25,6 +25,11 @@ IterativeRobot::IterativeRobot() {
  * the DS packets.
  */
 void IterativeRobot::StartCompetition() {
+  RobotInit();
+
+  // Tell the DS that the robot is ready to be enabled
+  HAL_ObserveUserProgramStarting();
+
   // Loop forever, calling the appropriate mode-dependent function
   while (true) {
     // wait for driver station data so the loop doesn't hog the CPU