RC_Channel: added secondary rudder support

this is used when nose wheel steering needs different reverse/range
from rudder
Plane: added secondary rudder support
Copter: CH6 tuning definition clean-up

Renamed and reorganised the CH6 #defines and parameter definitions
Copter: rename g.pid_throttle to g.pid_throttle_rate

Small code clean-up to make throttle rate controller's pid more obvious
Rover: update version for new release
Rover: added LEARN_CH parameter

this allows the learning channel to be set, for transmitters where
setting up channel 7 is difficult
Rover: changed to 2.43beta1
MAVLink: update to latest upstream message defintions XML

this adds new HIL support for airspeed, and common SIM_STATE and
RADIO_STATUS messages
Plane: update takeoff course when conditions met

This allows for change of heading before the final takeoff conditions
are met

thanks to Greg Fletcher for suggesting this
Plane: update FS_LONG_ACTN and FS_SHORT_ACTN docs

thanks to Craig for noticing this
Fix test_ins

Fix output format of test_ins and fix the number of parameters passed
to printf
AP_Baro: more precise altitude calculation on PX4

if not using an AVR CPU then use a more computationally expensive
altitude calculation, which is more precise at higher altitudes
AP_Baro: added units to baro documentation
AP_Baro: added get_EAS2TAS()

this provides the scaling factor between equivalent and true airspeed
based on altitude
AP_TECS: first implemention of TECS altitude control library
Plane: added new TECS altitude controller

Includes improvements to takeoff/launch detect logic to support hand
launching for X-8 flight
AP_AHRS: added airspeed_sensor_enabled() function
AP_SpdHgtControl: added speed/height control interface

this will be used by TECS
Plane: changed to using a "aircraft parameters" structure

this structure can be passed to libraries to give them easy access to
critical user parameters
AP_TECS: updates to use new aircraft parameter structure