AP_NavEKF : Fix bug in reset of GPS glitch offset

The GPS glitch offset was being zeroed during position resets. This caused the filter to reject subsequent GPS measurements if the GPS error persisted long enough to invoke a timeout and a position reset.
Copter: use define for pre-arm compass offset check
AP_GPS: Adding support for the NEO7 GPS
Tri: _min_throttle interpreted as 0~1000 range for throttle_lower flag

limit.throttle_lower flag becomes true when the throttle passed into the
motors lib (which is in the 0 ~ 1000 range) is below _min throttle.
This makes the interpretation of the THR_MIN parameter consistent
between the main code (which uses 0 ~ 1000 range) and the motors lib
(which previously used the RC3_MIN ~ RC3_MAX range).
The remaining problem however is that the output of the motors continues
to use THR_MIN as if it were a pwm.  I don't believe this is a dangerous
problem however.
MotorsMatrix: _min_throttle interpreted as 0 ~ 1000 range for throttle_lower flag

Also trigger throttle_upper flag when throttle in reaches 1000
SingleCopter: set throttle upper and lower flags
CoaxCopter: set throttle upper and lower flags
AC_AttControl: remove some old comments
AC_PosControl: remove completed to-do comments
Copter: ReleaseNotes for AC3.2-rc11
HAL_Linux: support direct UDP output from UART drivers

this allows safe operation over WiFi links without MAVProxy
Tracker: add nav_status comments

no functional impact
Tracker: check target of manual control msgs
Tracker: add vehicle struct comments

No functional change
Tracker: remove unused relative_alt
Tracker: move vehicle pos estimate to separate function
Tracker: move bearing and dist calcs to separate function
Tracker: move auto, manual and scan to separate files
Tracker: move pos estimate to separate function
Tracker: move servo control to servos.pde file