demonstrate ZMP tracking error
more accurate labeling of tests
experimental support for non-unit costs in ZMP closed form
Remove links from old collision filter groups

... when ignoring self collisions. Otherwise, self collisions will still be
checked between bodies that belong to collision filter groups eligible for
collision.
Add ignoreSelfCollisionsTest.
update closed ZMP solution to support non-unit costs, and add tests
only check size along first dimension
clean up
Don't use bullet if use_bullet is false
make sure frame_id is the right shape (column, not row)
visualizer remembers its position on the screen
handle R2012b missing flip() command
fix to the spring gradients
Merge pull request #618 from avalenzu/akv-fix-ignore_self_collisions

Fix a bug handling the ignore_self_collisions option to RBM
Merge pull request #620 from avalenzu/akv-fix-use_bullet

Don't use bullet if use_bullet is false
Merge pull request #622 from rdeits/rd-slider-position

visualizer remembers its position on the screen
Merge pull request #619 from rdeits/rd-test-zmp-tracker

Clean up and clarify ZMP closed-form solution
Merge pull request #624 from blandry/springgradfix

Fix to the spring gradients
implements an active set method for LCP time-stepping using the fastQP algorithm
better comments around reduced LCP logic