use ros::Time::now() if time lag exceeds threshold
Merge branch 'master' of https://github.com/uos/phidgets_drivers
add some hints to error message

I just spent 30 minutes trying to figure out why the IMU works on one
computer and doesn't on another one. Felt a little foolish when I found
out that the udev rules weren't installed; maybe providing some more
info in the error message helps others.
Merge branch 'update_errmsg' of https://github.com/uos/phidgets_drivers
Merge branch 'master' into fuerte