[boost] [config] gcc-4.8 and __GXX_EXPERIMENTAL_CXX0X__

Hi, it seems that gcc-4.8 doesn't defines any more __GXX_EXPERIMENTAL_CXX0X__ when the flag -std=c++11 is given. This means that all the BOOST_NO_CXX11_ are defined. Could something be done to make usable gcc-4.8 in c++11 mode? Best, Vicente