[PATCH] Deprecate external use of libio.h and _G_config.h.

[Florian Weimer]

* Zack Weinberg:

> +#if !defined _BITS_LIBIO_H && !defined _G_CONFIG_H
> +#error "Never include <bits/_G_config.h> directly; use <stdio.h> instead."
> +#endif

I think the #error should be indented.  This applies to two other
cases as well.

I reviewed the changes and checked that they do not cause material
changes on i386 (when compiled with -DNDEBUG).  Test suite is clean as
well.  With the formatting fix above, this should be okay.  Thanks.