APM_Control : Moved scaler on roll and pitch integrator to be before integrator

This means that the value of aileron and elevator trim offset won't change with airspeed
Plane: tag 2.75beta5
HAL_PX4: prevent threads running before subsystems are initialised

this fixes a bug where the timer thread would hang waiting for the
console on startup. This caused the "hit enter" behaviour with recent
PX4 bugs, as AnalogIn tried to read from fd==0, which was a console
read
HAL_Linux: fixed scheduler initialisation bug in Linux HAL as well
AP_InertialNav: add comments, rename incorrectly named member,
initialize member, remove redundant assignment
adjustments to original commit by randy
AP_InertialNav: remove unused AP_InertialSensor pointer
Copter: add comment (unit of G_Dt)
AP_Baro: add time-unit comment
Filter: add consts
AC_Sprayer: add consts, update comments

* removed some comments that were left over from the classes this class
was copypasta'ed from
Copter: Log.pde: replace unused copy with ref (saves again some bytes)
AC_Sprayer: replace unnecessary object with const ref
AC_WPNav: replace unnecessary objects with const refs
AC_Sprayer: add doxygen info
Copter: use const refs instead of unneeded copies
AC_Fence: make member pointer to AP_InertialNav const, remove unused
gps-pointer member
AC_Fence: replace "_ina->geT_position().z" with more efficent
"_inav->get_altitude()"
AC_WPNav: make member pointer to AP_InertialNav object const since it's
never modified
AC_WPNav: make more member pointers const
AP_InertialNav: move variable definitions to elide unused default
construction of objects (saves 106 bytes)