FastSerial: add extra example sketch MultiFastSerial to test multiple ports

libraries/FastSerial/examples/MultiFastSerial/Makefile

+BOARD	=	mega
+include ../../../AP_Common/Arduino.mk

libraries/FastSerial/examples/MultiFastSerial/MultiFastSerial.pde

+// -*- Mode: C++; c-basic-offset: 8; indent-tabs-mode: nil -*-
+
+//
+// Example code for the FastSerial driver.
+//
+// This code is placed into the public domain.
+//
+
+//
+// Include the FastSerial library header.
+//
+// Note that this causes the standard Arduino Serial* driver to be
+// disabled.
+//
+#include <FastSerial.h>
+#include <AP_Common.h>
+/* Not required by this sketch, but required by AP_Common */
+#include <AP_Math.h>
+
+//
+// Create a FastSerial driver that looks just like the stock Arduino
+// driver, on each serial port.
+//
+FastSerialPort0(Serial);
+FastSerialPort1(Serial1);
+FastSerialPort2(Serial2);
+FastSerialPort3(Serial3);
+
+
+void setup(void)
+{
+        //
+        // Set the speed for our replacement serial port.
+        //
+        Serial.begin(115200);
+        Serial1.begin(115200);
+        Serial2.begin(115200);
+        Serial3.begin(115200);
+
+        //
+        // Test printing things
+        //
+        Serial.print("test");
+        Serial.println(" begin");
+        Serial.println(1000);
+        Serial.println(1000, 8);
+        Serial.println(1000, 10);
+        Serial.println(1000, 16);
+        Serial.println_P(PSTR("progmem"));
+        Serial.printf("printf %d %u %#x %p %f %S\n", -1000, 1000, 1000, 1000, 1.2345, PSTR("progmem"));
+        Serial.printf_P(PSTR("printf_P %d %u %#x %p %f %S\n"), -1000, 1000, 1000, 1000, 1.2345, PSTR("progmem"));
+        Serial.println("done");
+        
+        Serial1.println("hello serial1");
+        Serial2.println("hello serial2");
+        Serial3.println("hello serial3");
+
+}
+
+void
+loop(void)
+{
+    int    c;
+
+    //
+    // Perform a simple loopback operation on each port.
+    //
+    c = Serial.read();
+    if (-1 != c)
+        Serial.write(c);
+
+    c = Serial1.read();
+    if (-1 != c)
+        Serial1.write(c);
+
+    c = Serial2.read();
+    if (-1 != c)
+        Serial2.write(c);
+    
+    c = Serial3.read();
+    if (-1 != c)
+        Serial3.write(c);
+}