Subtracts off margin for raycasts onto box/mesh.

Thanks Andres! Depth sensors in drake should now be a lot more
accurate.
Taking away margins entirely
Merge branch 'master' of https://github.com/RobotLocomotion/drake into lidar_fix_pure
Ability for rigid mody manip to toggle margins in collision detects

Rigid Mody Manipulator now maintains two bullet collision models, one with margins on
meshes and boxes, and one without. Boolean flags on collision-relevant methods
(which currently default to true, i.e. with margins like previously) allow control
on per-call basis.
Merge branch 'master' of https://github.com/RobotLocomotion/drake into lidar_fix_pure
Fixing function ambiguity that is causing model_test ot fail.

As far as I can tell, given the new AddElement variants with an extra optional
bool arg, the compiler was deciding that casting the (also optional, through
multiple function declarations) group_name string could be cast to a bool
to make the call work... resolved by changing the version of the call without
the groupname supplied to have its own special name. (Hopefully this doesn't
affect anyone outside of model_test?
Merge branch 'master' of https://github.com/RobotLocomotion/drake into lidar_fix_pure
Prepping for hackathon
Merge branch 'master' of https://github.com/RobotLocomotion/drake into lidar_fix_pure
Removing addElementWithoutGroup

DrakeCollision model can no longer have an element added without
a group specified. If you don't want to specify one, you can
use default, even though I guess that still means you're
specifying / choosing one. This functionality was used in
a single test and no other part of Drake.
Reverting spoilers

This belongs to an incomplete feature
Collision raycast defaults to more accurate setting
Merge pull request #481 from gizatt/lidar_fix_pure

Subtracts off margin for raycasts onto box/mesh