AP_HAL: added double print functions

this copes with the fact that the compiler doesn't really know that
float and double are the same things

libraries/AP_HAL/utility/Print.cpp

@@ -91,6 +91,14 @@ size_t Print::print(float n, int digits)
   return printFloat(n, digits);
 }
 
+// the compiler promotes to double if we do arithmetic in the
+// argument, but we only actually want float precision, so just wrap
+// it with a double method
+size_t Print::print(double n, int digits)
+{
+	return print((float)n, digits);
+}
+
 size_t Print::println(void)
 {
   size_t n = print('\r');
@@ -154,6 +162,14 @@ size_t Print::println(float num, int digits)
   return n;
 }
 
+// the compiler promotes to double if we do arithmetic in the
+// argument, but we only actually want float precision, so just wrap
+// it with a double method
+size_t Print::println(double num, int digits)
+{
+  return println((float)num, digits);
+}
+
 // Private Methods /////////////////////////////////////////////////////////////
 
 size_t Print::printNumber(unsigned long n, uint8_t base) {

libraries/AP_HAL/utility/Print.h

@@ -57,6 +57,7 @@ class AP_HAL::Print {
     size_t print(long, int = DEC);
     size_t print(unsigned long, int = DEC);
     size_t print(float , int = 2);
+    size_t print(double , int = 2);
 
     size_t println(const char[]);
     size_t println(char);
@@ -66,6 +67,7 @@ class AP_HAL::Print {
     size_t println(long, int = DEC);
     size_t println(unsigned long, int = DEC);
     size_t println(float , int = 2);
+    size_t println(double , int = 2);
     size_t println(void);
 
 };