Merge pull request #280 from erwincoumans/master

Minkowski Portal Refinement, Finite Element Method demo
fix linux build of test/collision
Merge pull request #281 from erwincoumans/master

comment-out the memset in DEBUG mode in btVector3.cpp and b3Vector3.cpp
fix a problem in the btMultiBodyConstraint related to self-collision, see also
https://github.com/bulletphysics/bullet3/issues/290
prepare to create coordinate frame demo, minor cleanup for create funcs in demo entries,
fix r2d2.urdf inertia
Merge remote-tracking branch 'upstream/master'