restored gcc4.6 compatibility on MacOS
restored gcc4.6 compatibility on MacOS

silgon/rlpy,BerkeleyAutomation/rlpy,MDPvis/rlpy,silgon/rlpy,silgon/rlpy,imanolarrieta/RL,BerkeleyAutomation/rlpy,rlpy/rlpy,MDPvis/rlpy,BerkeleyAutomation/rlpy,rlpy/rlpy,imanolarrieta/RL,rlpy/rlpy,MDPvis/rlpy,imanolarrieta/RL