Failsafe events changed to errors so they are more obvious.
Errors recorded to dataflash for failure to init compass and optical flow sensor.
Errors recorded for pwm failure.
Resolved a compile error when dataflash logging is disabled.

Note: not yet enabled as part of any flight mode

ArduCopter: turn on INERTIAL_NAV_Z in the config.h file so that it takes effect when built for the mission planner

ArduCopter: Battery failsafe triggers RTL only if we are more than 15m from home, otherwise it performs a LAND

Bug fix from Leonard.

All changes by Sandro Benigno

Updated AP_Camera class.

Thanks to Jonathan for this.

ArduCopter: bug fix to GUIDED mode.  Now checks that desired altitude was reached before deciding the waypoint is complete.

ArduCopter: add AUTO_VELZ_MIN, AUTO_VELZ_MAX and PILOT_VELZ_MAX to allow better control of climb/descent rate in auto and manual throttle modes

GPS_PROTOCOL_MTK16
to
GPS_PROTOCOL_MTK19

ArduCopter: move gcs_check function (which sends to ground station) to run when 50hz loop is not running

Also removed redundant heartbeat message