A little more digging and I found this:
http://www.boost.org/doc/libs/1_47_0/libs/filesystem/v3/doc/reference.html#path-deprecated-functions
I guess you probably found it also but posting here since it takes some searching to find it.
Not sure what the difference is between native_string() and string(). I'm unfamiliar with the documentation structure and I got lost trying to find the specifics on those functions. But it does seem like string() is the one they want you to use.
I don;t know who I would speak to about getting this fixed in the git version ? or weather the have left it like that for backward compatibility ?