[boost] [c++0x] cpp0x branch created, config macros added

A branch has been created for C++0x related work. See svn.boost.org/svn/boost/branches/cpp0x I've added 15 macros that describe C++0x features not supported, along the lines discussed in previous threads. Since these changes will force compiles for all libraries that use Boost.Config, I'd like to be sure they are stable on the branch before merging to trunk and eventually release. Please inspect the changes and give them a try. This branch is also intended to act as a common development location for the new C++0x clock/time_duration/time_point supporting infrastructure. Specifically common_type and ratio. Comments appreciated, --Beman