fix for grad with pos control and test
Use btConvexHullShape for boxes.

The convex interface that we're using for our closest-distance computations
gives erroneous normals for box shapes. If we represent the box as the convex
hull of its vertices the normals are fine. Fixes #174.
Add test case for box-point contact normals
Update contactImplicitBrick test.

Changes:
  * Removes terrain-only flag.
  * Disable visualization by default
  * Check positions and velocities with different tolerances (as per Michael's
    email)

Now passes with tolerances 1e-2 for positions 1e-1 for velocities.
resolves megaclear crashes.  horrah.  finally figured out that the problem was that constructModelmex was being cleared, therefore destroying the memory allocated with it, before the delete function was being called (at least on some platforms).  added mexLock and mexUnlock logic to protect against this.
apply fix to IKoptions mex
changed variable name as suggested by Hongkai
Merge pull request #268 from RussTedrake/memory_fix

Resolves at least one BIG memory bug.  hoorah
Fixed bug in RigidBodyTorsionalSpring where spring torque was only applied to the child body (and not the parent).
Merge branch 'drake-origin/master'
removed persistent variable
fixed typo
Merge pull request #271 from kuindersma/fix-poly-no-mail-typo

fixed typo in AffineSystem
Changed quat methods to return a value instead of working with references.
drakeQuatUtil --> drakeGeometryUtil.
Merge pull request #272 from tkoolen/drakeQuatUtil-updates

Drake quat util updates
fixed typo causing quadrotor unit test to fail
Merge branch 'poscontrol' of https://github.com/blandry/drake
use valuecheck in test
Slightly increase tol in contactImplicitBrick.