Similar to commits 1686f4e8 and
30a5dd26

The former is deprecated by C++14. The standard says they are the same:

The header defines all types and macros the same as the C standard library
header<stdint.h>.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

The former was deprecated with C++14.

According to the C++11 and C++17 standards, both files are identical.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Since we switched from autotools to Meson in commit
94592c14, we don't need to include
`config.h` early to properly enable large file support.  Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.

This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.

Migrate callers to GetSocket().Read(), GetSocket.Write(), which is the
same.

Remove the const_cast from HttpdClient.cxx, and avoid one allocation
in ClientRead.cxx.

Replaces GLib's GError.

BufferedSocket has just an input buffer, and FullyBufferedSocket adds
the output buffer.