AP_SpdHgtControl: added new path_propportion var

libraries/AP_SpdHgtControl/AP_SpdHgtControl.h

@@ -70,6 +70,9 @@ public:
 	// return landing sink rate
 	virtual float get_land_sinkrate(void) const = 0;
 
+	// set path_proportion accessor
+    virtual void set_path_proportion(float path_proportion) = 0;
+
 	// add new controllers to this enum. Users can then
 	// select which controller to use by setting the
 	// SPDHGT_CONTROLLER parameter