this will prevent us losing a lot of altitude during the initial
failsafe phase

thanks to Doug for this fix!

this makes the PID library a bit more flexible for smaller range
numbers. Note that this library is used on ArduPlane and Rover, not
Copter

this removes a lot of the old arduplane code, and renames a lot of
variables.

This will need a lot more testing and fixup before being usable

used to launch nsh for PX4IO firmware upgrades

Corrected "it's" to "its". Just one of those grammar things that drives me crazy ;-)

this changes the sampling to 200Hz regardless of requested rate, and
it is downsampled inside num_samples_available() using a shift. This
gives better noise resistance in ArduPlane.

This patch also makes it possible to update the filter frequency while
running, which is very useful for bench testing with a vibration
source

bitwise, not arithmetic

- libraries/AP_Common/AP_Common.h: Use bit 2 of Location.options to store
  loiter direction
- ArduPlane/defines.h: New bitmask MASK_OPTIONS_LOITER_DIRECTION for struct
  Location bit 2
- ArduPlane/ArduPlane.pde: New variable loiter_direction
- ArduPlane/GCS_Mavlink.pde: For mavlink loiter-commands use sign of param3 to
  detemine direction. Set Location.option flag accordingly
- ArduPlane/commands.pde: Make sure loiter-directions get saved into EEPROM
  correctly
- ArduPlane/commands_logic.pde: Set loiter_direction on all loiter-actions
  as well as RTL/instant loiter
- ArduPlane/navigation.pde: Yield loiter_direction in update_loiter

After Plane: cleanup driver declaration 4d9a74d7, HIL_MODE_ATTITUDE with MAG_ENABLE=1 set results in continuous reboot/APM crash.  Added define for AP_COMPASS_HIL when HIL_MODE_ATTITUDE is enabled.

this saves a couple of hundred bytes of flash.

This reverts commit 527dcdf3.

This was causing the MPU6000 startup code to fail, due to time running
backwards.

* Smokey, this is not 'Nam. this is bowling. there are rules

- More efficient code by using 16-bit timer
- micros() now has proper 1 us resolution and less overhead
- millis() has less overhead
- removed unneeded/unwanted initializatin of timers in AVRTimer::init()

pull request 62, approved and merged by pat

Scaling of bottom half of throttle was changed from THR_MIN ~ 500.
Previously it was from 0 ~ 500.

Accel throttle's I term is taken from scaled manual throttle