APM_Control: added STEER2SRV_MINSPD

this is the assumed min speed when in STEERING or AUTO mode
Rover: smooth steeing at low speed in STEERING mode

use the G limit from the turn radius as the steering limit
Rover: prep for 2.45beta6
AP_HAL: implement AP_HAL::MemberProc via FastDelegate.h

this provides a more portable way to encapsulate member functions in
variables
HAL_AVR: updates for AP_HAL::MemberProc
HAL_FLYMAPLE: updates for AP_HAL::MemberProc
HAL_Empty: updates for AP_HAL::MemberProc
HAL_AVR_SITL: updates for AP_HAL::MemberProc
HAL_Linux: updates for AP_HAL::MemberProc
HAL_PX4: updates for AP_HAL::MemberProc
AP_InertialSensor: updates for AP_HAL::MemberProc
AP_OpticalFlow: updates for AP_HAL::MemberProc
DataFlash: updates for AP_HAL::MemberProc
AP_Baro: updates for AP_HAL::MemberProc
AP_Airspeed: updates for AP_HAL::MemberProc
AP_ADC: updates for AP_HAL::MemberProc
Rover: updates for AP_HAL::MemberProc
Copter: updates for AP_HAL::MemberProc
Plane: updates for AP_HAL::MemberProc
Plane: removed some compat code

fixes warnings