svn cat boost/version.hpp
git show HEAD:boost/version.hpp
The HEAD here is the revision of the current branch. So svn cat -r PREV boost/version.hpp would be
git show HEAD^:boost/version.hpp
and the version three revisions ago
git show HEAD~3:boost/version.hpp
svn revert boost/version.hpp
git checkout boost/version.hpp
This removes any local changes to a file and replaces them with the last-committed version.