Copter: alt hold feed forward filter
APM_Control: neaten up code formatting
Plane: zero attitude integrators on the ground
APM_Control: cope with zero integrator or tconst

if the user zeros the integrator tuning factor, we need to zero the
integrator
Plane: reset attitude integrators on mode change
AutoTest: reduce circle test time
Rover: updated AUTO_TRIGGER_PIN docs
Copter: guided mode yaw fix

Nose of copter now points at next guided point if it is more than 10m
away
rtl resets yaw to same as when armed - unless user specifies otherwise
changed yaw reset to when armed to not use initial_simple_bearing
Copter: remove unused print_wp function
failsafe gps lost bug fix
Copter : Land submode - Check for GPS 3D Fix instead of checking for available home position
Copter : POSITION_HOLD mode -> allow user position control
Copter: update firmware version and release notes
Copter: updated AC3-rc4 release notes
PX4: added eagletree I2C airspeed driver to the NuttX build

just needs a wrapper driver in APM now
AP_Param: fixed parameter save bug

This bug affected parameters where the defaults are overridden in the
object constructor. For example, a PID object may have a default value
for PID_D of 0.0, but have a constructor based default of 0.2. If the
user tries to set the value to exactly 0.0, then the set wouldn't happen,
as the value matches the value in the object default var_info[]
table. 

This change ensures we force a save to eeprom if the value is changing
from the current value, regardless of the var_info[] default.

Thanks to Tom Coyle for finding this bug!
Rover: move to beta2
Copter: reduce pre-arm board voltage check to 4.3V