remove warnings

We've been piling up warnings for a while, and I was too burnt out for real thinking work, so I decided to remove some of the warnings on linux.

Added fix for a bug that Clement noticed:  when you teleport the new "measured velocity" system would compute a very large velocity caused by the jump to new location, and so your avatar would skid past its intended arrival point.  When jumping around we need to also clear the avatar's position and velocity history.