Copter: update FS_THR_VALUE parameter description

One user was setting FS_THR_VALUE too low, below 900 which means
ArduCopter would not trigger when the ppmencoder pulled ch3 low after
updates from the ppmencoder stopped
Rover: update FS_THR_VALUE parameter description
Plane: update THR_FS_VALUE parameter description
autotest: fixed import of mavwp
autotest: added $HOME/APM to PYTHONPATH
autotest: update timeout again

we're getting too close
Copter: show pilot input in dataflash ATT message even when in AUTO

AUTO mode ignores pilot input but we still want to be able to see the
pilot's input in the Roll-In and Pitch-In columns of the dataflash's ATT
message
Copter: increase default CIRCLE_RATE to 20deg/sec
Plane: param description change for RC5 ~ RC11

Reversing the order may avoid duplication of param descriptions in the
auto generated parameter web page
APM_Control: Pitch Control - Reduced the speed below which the integrator is locked

This is to allow for slow speed flare manoeuvres in FBW modes
APM_Control: Added integrator limiting adjustable by an advanced user parameter

this is compatible with the old IMAX settings
Plane: Added APM_Control integrator limits to table used to covert old PID values
Copter: minor param definition unit changes
PX4: use PX4_ROOT=../PX4Firmware by default

this should make PX4 builds work out of the box on Windows for people who have used
the github for windows tool to download the two repositories
Plane: APM2 doesn't have channel 9 PWM output
autotest: consider lack of symlinks to be a soft error

some people use VMWare shared drives, which don't do hard links
PX4: added ARDUPILOT_BUILD define

will be used to avoid some code in the px4io driver
PX4: log devices being used in boot.log
AP_Relay: added RELAY_PIN parameter

makes it easier to choose a pin
AP_Camera: added CAM_TRIGG_DIST parameter

for triggering every N meters of GPS distance travelled