Worked around MSVC 10 compilation error. The compiler fails to resolve overloaded add_value functions when the attribute value is a string literal.

git-svn-id: http://svn.boost.org/svn/boost/trunk@84194 b8fc166d-592f-0410-95f2-cb63ce0dd405
Added a note about minimal supported 32 bit x86 CPU.

git-svn-id: http://svn.boost.org/svn/boost/trunk@84195 b8fc166d-592f-0410-95f2-cb63ce0dd405