libio bugs

[H.J. Lu]

> 
> This patch fixes some bugs in libio.
> 
> Btw, why does _IO_wchar_t in streambuf.h default to short and not
> _G_wchar_t?  And why does ios::fill(_IO_wchar_t) cast its argument to
> char?  Unfortunately, changing that now breaks binary compatibility on
> Linux.
> 

We can still change it for glibc 2.1. glibc 2.1 will change the
iostream ABI. glibc 2.1 has

#define _G_IO_IO_FILE_VERSION 0x20001

in _G_config.h. It can be used to identify glibc 2.1.


H.J.