basic_stringbuf functional

[Christof Petig]

Hi,

basic_stringbuf is now functional (writing tested, reading should work
though)

If there are any problems with us gaining also copyright to our file,
please contact me. Though with a GPLed program, usually there aren't.
I'm no lawyer to get all implications of your license.

I used no buffering, though [lib.stringbuf.virtuals] mention gptr() and
pptr().
IMHO this is the best solution. Feel free to discuss that with me.

Enjoy
    Christof

PS: Is there any way to get access to a current source tree? I might
want to fill some stubs within streambuf & Co.
PPS: initializing the streambuf pointers to zero is necessary for
stringbuf to work!
sstream.diff.gz