fix bug: SkeletonDynamics::setInternalForces(...) set the internal forces as zero always because the default values of internal forces's min/max allowance was zero. Now the default values are -1e9 and 1e9.
fix bug: SkeletonDynamics::setInternalForces(...) set the internal forces as zero always because the default values of internal forces's min/max allowance was zero. Now the default values are -1e9 and 1e9.
Changing World class interface.
replace 1e9 to std::numeric_limit<double>::infinity()
Merge remote-tracking branch 'refs/remotes/origin/master' into gazebo_support

Conflicts:
	src/simulation/World.cpp
merge from master branch
Merge pull request #55 from dartsim/gazebo_support

Gazebo support