patch - implementation of stdio_fstream

[Benjamin Kosnik]

>Here we go the legal stuff shold all be taken care off now. Here is the
>patch implementing an extension to hook the stdio_filbuf up with an
>stdio_fstream. This allows people to hook streams up to pipes
>(initialization with fd) and FILE*. Both use cases are really useful but
>no longer supported by the C++ standard. 

Ok, your assignment just came through, so putting this in is now a
possibility. Thanks again for your patience. 

-benjamin