Ensured correct pointer init
Hotfix: Made accel calibration a bit more forgiving about motion threshold
Merge branch 'auth' of https://github.com/PX4/Firmware into px4_master
I added support for signing and verifying Serial data to create and verify a "Certificate of Authenticity"  data block that will ( soon ) be written to One-Time-Programmable Flash.
usage:\n"
auth [-x] [-p] [-d] [-w] [-k] [-v] [-l] \n"
  -x     Read Private Key from /mnt/microsd/privatekey.px4 and display it
  -p     Read Public Key from  /mnt/microsd/publickey.px4 and display it
  -c     make a Certificate-Of-Authenticity with the private key and display it ( assumes also -x )
  -w    write the Certificate-Of-Authenticity to Flash ( assumes also -x and -c )
  -k     LOCK the Certificate-Of-Authenticity to ONE-TIME-PROGRAMMABLE Flash PERMANENTLY ( assumes -w -x -c )
  -v     Verify the Certificate-Of-Authenticity in OTP with the public key, and display results.  ( assumes -p )
  -t     test cert-of-auth just generated without OTP ( equivalent to -x -p -c -v )
  -l     log it.  Append the COA and privatekey info to the SD card at /fs/microsd/OTPCertificates.log
  -h     use Hardcoded Private/Public Keys, no SD card needed
  -s     use hardcoded serial: '33002E 32314704 34303736'

TODO:   -w and -k are not really implemented yet.   also reading vert straight from OTP isn't implemented yet ( we fake it by using -t -l and then reading from SD card for now).
certificate files use .txt, as .px4 was a poor choice of extension as its already used elsewhere.
WIP for OTP integration - looks OK, but not working yet.