Defensive driving PR

[dfridovi]

@chihyuanchiu can you clean up and open a PR to merge the defensive driving branch into master? I thought it was already in there but evidently it's not...

[dfridovi]

@chihyuanchiu your latest commit seems to have broken a ton of the examples. Try running skeleton_example now and it totally breaks.. I have to revert to 4ec2ea7 to get it to even run past the first commit (needs an --initial_alpha_scaling=0.3 modification even there to run correctly). I reverted your previous merge (5bff5dd). Before making any changes to master, please open a PR from your branch to master and confirm that all examples still run reasonably well.