Plane: fix auto doc unit on GROUND_STEER_DPS
Tools: Update gcc-arm version from q2 to q4

This fixes the installation script since version q2 has been removed
from launchpad.
build: fix paths in install-prereqs-ubuntu.sh

Also upgrade to the latest 2013q4 "GNU Tools for ARM
Embedded Processors" toolchain since the 2012q2 release
is no longer available for download.
Parachute: initial draft library
RC_Channel: add parachute_release to function enum
AP_Parachute: add example sketch

Only tests that the lib compiles
Copter: integrate parachute lib
Copter: extend crash check to trigger parachute
Copter: ch7/ch8 parachute release
AC_AttControl: return angle_ef_targets as const ref
Copter: add min alt check to parachute release
GCS_MAVLink: add MAV_CMD_DO_PARACHUTE
GCS_MAVLink: generate after MAV_CMD_DO_PARACHUTE added
Mission: add support for MAV_CMD_DO_PARACHUTE
Copter: process MAV_CMD_DO_PARACHUTE commands
Parachute: minor comment changes
Copter: log parachute events
Notify: add parachute release tune for Pixhawk
Parachute: set AP_Notify parachute_release flag
Parachute: add AP_Notify.h to example sketch