Branch for Iostreams development

svn path=/branches/iostreams_dev/boost/detail/lcast_precision.hpp; revision=42144
Initialized merge tracking via "svnmerge" with revisions "1-42143" from 
https://svn.boost.org/svn/boost/trunk

svn path=/branches/iostreams_dev/boost/implicit_cast.hpp; revision=42428