[Patch] Simplify basic_streambuf::setg() and setp()?

[Benjamin Kosnik]

>The point is: I have checked the standard and a couple of
>other implementations and cannot find support for the final
>'if' of our current setg() and setp().

Then how does pubsetbuf work? If you test this, you'll find test results
that fail, as we try to keep the v2 implementation-defined behavior here.

-benjamin