Copter: bug fix to look_ahead_yaw

Fix received from David Dewey
Was incorrectly using the direction instead of heading when deciding
whether to point forward or not.  Reduced YAW_LOOK_AHEAD_MIN_SPEED to
1m/s because bug meant it was nearly always pointing forward and 10m/s
(the old value) seemed too high
Plane: use new scheduler load_average() function

this also simplifies the main loop
Copter: use the new scheduler load_average() call

this also simplifies the main loop
Rover: use the new load_average() API
Plane: make it easier to find task numbers
Plane: run TECS 50Hz code when throttle suppressed

this fixes auto-launch detection using TECS
Plane: use a larger serial buffer

this makes higher rate MAVLink possible again
Copter: ask for IMU samples at 100Hz

this produces the same result, but makes things simpler in the driver
AP_TECS : Improvements and bug fixes to feed-forward throttle demand

This fixes a bug in the feed-forward throttle that prevented the bank to throttle compensation from working properly during descents.
It also adds bank to throttle compensation to the non-airspeed sensor throttle algorithm.
AP_L1_Control : Fixed bug in track capture angle limit
APM_Control: rename 'stabilize' to 'disable_integrator'

this better reflects what it does
Plane: allow integrator in stabilize mode when no stick input

fixes issue #472
AP_Scheduler: prevent a divide by zero
Plane: fixed build with OBC failsafe
AC_Fence: remove unused gps pointer
AP_Math: use const references not pointers for location functions

this makes life a bit easier for the new AP_Mission library

Pair-Programmed-With: Brandon Jones <brnjones@gmail.com>
AP_Limits: fix for new AP_Math API

Pair-Programmed-With: Brandon Jones <brnjones@gmail.com>
AP_L1_Control: fix for new AP_Math API

Pair-Programmed-With: Brandon Jones <brnjones@gmail.com>
AP_InertialNav: fix for new AP_Math API

Pair-Programmed-With: Brandon Jones <brnjones@gmail.com>
AP_Camera: fix for new AP_Math API

Pair-Programmed-With: Brandon Jones <brnjones@gmail.com>