[sim] fix symbolic link
[log/replay] this should allow to replay logs including procedures

fix #227
adjusted scaling of ezcurrent sensor
[modules] minor cleanup of ezcurrent sensor
[gps] update doxygen comment
[peripherals] adxl345_spi: set in/out length to fixed 7 again, mixed lenght not working reliably
[rotorcraft] print info if using FAILSAFE_GROUND_DETECT
[peripherals] hmc58xx: fix typo in comment and make explict separate defines for Y,Z data regs for HMC5843/HMC5883
[stm32][spi] select slave after configuring clock/phase, etc of peripheral
Also:
- replace tx_length_case by simpler use_dummy_tx_buf
- minor comment cleanup while here...
[imu] correct mag axes for aspirin_v1.5. RECALIBRATE!!!
[rotorcraft] separate KILL_ON_GROUND_DETECT with higher default threshold
- if KILL_ON_GROUND_DETECT is TRUE, enable killing of motors on ground detection
  used in default land block, add to your airframe file:
  <define name="KILL_ON_GROUND_DETECT" value="TRUE"/>
- THRESHOLD_GROUND_DETECT is now in m/s^2 and defaults to 25 m/s^2
[sw/ext] update libopencm3 to get missing systick_get_reload declaration
[stm32] fix sys_time_usleep, sorry about that...
[tests] test prog for sys_time_usleep
[conf] change warnings about obsolete subsystems to errors
[conf] update mag calib and imu orientation in quadrotor example
[sys_time] no more macros, clenup
should also result in performane improvements since ticks, etc.
are calculated at startup and usec conversions are only fixedpoint now
[sys_time] I hate integer arithmetic with it's overflows...
maybe we should do all the conversions in 64bit and convert back to 32?
[lpc21] fix compilation of servos
We should really use less macros...
[gen] Raise error when unit conversion should have been performed but failed silently (e.g. when adding a space after a float)