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.
Slightly increase tol in contactImplicitBrick.
Use rel. tol. 1e-8 in ModelTest.cpp
more info in knownIssue because some known issues are reporting as unknown
Merge pull request #267 from avalenzu/fix-contact-normals

Fix contact normals
<exception> --> <stdexcept>
found a unit test that wasn't actually running.  (also had to fix the test, which was failing once it ran)
Merge branch 'master' of https://github.com/RobotLocomotion/drake
Merge pull request #276 from tkoolen/drakeGeometryUtil-additions

Drake geometry util additions
moved code style guide over to github wiki
Merge branch 'master' of https://github.com/RobotLocomotion/drake
Gradient function updates:
* {get,set}SubMatrixGradient can now handle non-contiguous rows and cols
* improved matGradMult for empty inputs
* added quadFormGrad + test
Added second derivative to normalizeVec.
Various gradient related functions.
Variable renames.
RBM utility functions.
jointQdotTov, jointVToqdot
testDHomogTransInv.