merged from trunk


[SVN r31944]
Fixed the converting assignment bug in optional<>
Fixed the usage of 'None' in converter.h, which is declared as a macro in X11/X.h


[SVN r32531]
Added simple operators << and >> to optional<>


[SVN r32533]
fix char set tag


[SVN r34548]
Boost.Log merged to trunk.

[SVN r83860]