Copter: add sanity check for ModeFollow requiring AC_Avoid

Copter: correct compilation when logging disabled

Copter: correct compilation when mount disabled

ArduCopter/Log.cpp

@@ -573,7 +573,6 @@ void Copter::Log_Write_Home_And_Origin() {}
 void Copter::Log_Sensor_Health() {}
 void Copter::Log_Write_Precland() {}
 void Copter::Log_Write_GuidedTarget(uint8_t target_type, const Vector3f& pos_target, const Vector3f& vel_target) {}
-void Copter::Log_Write_Proximity() {}
 void Copter::Log_Write_Vehicle_Startup_Messages() {}
 
 #if FRAME_CONFIG == HELI_FRAME

ArduCopter/autoyaw.cpp

@@ -160,7 +160,7 @@ void Copter::Mode::AutoYaw::set_roi(const Location &roi_location)
         //      4: point at a target given a target id (can't be implemented)
 #else
         // if we have no camera mount aim the quad at the location
-        roi = pv_location_to_vector(roi_location);
+        roi = copter.pv_location_to_vector(roi_location);
         auto_yaw.set_mode(AUTO_YAW_ROI);
 #endif  // MOUNT == ENABLED
     }

ArduCopter/config.h

@@ -668,6 +668,10 @@
   #error AC_Avoidance relies on AC_FENCE which is disabled
 #endif
 
+#if MODE_FOLLOW_ENABLED && !AC_AVOID_ENABLED
+  #error Follow Mode relies on AC_AVOID which is disabled
+#endif
+
 #if MODE_AUTO_ENABLED && !MODE_GUIDED_ENABLED
   #error ModeAuto requires ModeGuided which is disabled
 #endif