path and directory_iterator doesn't handle windows root path

[nobody]

directory_iterator does not append '\' to a windows
root path correctly.
The following Code

using namespace boost::filesystem;
path p("C:",native);
directory_iterator it(p);
is_directory(it);

throws an exception which says
"boost::filesystem::is_directory "C:some_file.foo": The
system cannot find the given file."
If I use C:\ it works. If I use a non root directory
like C:\some_directory it works too.

[beman_dawes]

Logged In: YES 
user_id=51042

Fixed and regression-test cases added, both head and i18n
branch.

Thanks for the report!