use memcheck_available_memory() instead of freeRAM()

this provides a more accurate view of memory

ArduCopter/system.pde

@@ -75,7 +75,7 @@ static void init_ardupilot()
 
 	Serial.printf_P(PSTR("\n\nInit " THISFIRMWARE
 						 "\n\nFree RAM: %lu\n"),
-						 freeRAM());
+                    memcheck_available_memory());
 
 
 	//
@@ -503,21 +503,6 @@ init_optflow()
 }
 #endif
 
-/* This function gets the current value of the heap and stack pointers.
-* The stack pointer starts at the top of RAM and grows downwards. The heap pointer
-* starts just above the static variables etc. and grows upwards. SP should always
-* be larger than HP or you'll be in big trouble! The smaller the gap, the more
-* careful you need to be. Julian Gall 6 - Feb - 2009.
-*/
-static unsigned long freeRAM() {
-	uint8_t * heapptr, * stackptr;
-	stackptr = (uint8_t *)malloc(4); // use stackptr temporarily
-	heapptr = stackptr; // save value of heap pointer
-	free(stackptr); // free up the memory again (sets stackptr to 0)
-	stackptr = (uint8_t *)(SP); // save value of stack pointer
-	return stackptr - heapptr;
-}
-
 static void
 init_simple_bearing()
 {