autotest: cope with slower updating roll in MAVLink for plane

need less precision in horizontal roll test
AP_GPS: fixed examples build
AC_Fence: fixed examples build
AC_WPNav: disabled broken example build

this test doesn't actually do anything yet
AP_AHRS: fixed example build
AP_Airspeed: fixed example build
AP_InertialNav: fixed example build
AP_Mount: fixed example build
DataFlash: fixed example build
Copter: bug fix for descent during loiter_turns
APM_Control: fixed YAW2SRV_IMAX handling

thanks to Steven G for noticing this!
Plane: fixed FBWB aileron control
Plane: prepare for 2.74b release
autotest: update plane test with more modes

added tests for FBWB, STABILIZE, CRUISE, ACRO and CIRCLE
AP_Motors: Added MOT_UNSAFE_THR parameter - Throttle setting used to signal that the copter is armed or otherwise unsafe to approach
Copter: Warn user with motors while copter is arming
Copter: Cancel arming if throttle input above cruise_throttle.
Copter: do not spin motors during arming process
Copter: renamed MOT_UNSAFE_THR to MOT_SPIN_ARMED

Removed special purpose spin_unsafe function
renamed _throttle_unsafe to _spin_when_armed and changed to an AP_Int8
Copter: implement safety spin for Tricopters