#include <cstddef> may declare size_t only in namespace std

[Kjell Ahlstedt <kjell ahlstedt bredband net>]

The following posts in libsigc-list discuss an issue that will affect 
not only libsigc++.

https://mail.gnome.org/archives/libsigc-list/2012-July/msg00007.html
https://mail.gnome.org/archives/libsigc-list/2012-July/msg00011.html

libsigc++, glibmm, gtkmm and perhaps other modules assume that '#include 
<cxxxxx>' (cxxxxx = cstddef, cstdlib, ctime, etc.) declares data types 
and functions in the global namespace. With gcc version 4.7 they are 
declared only in namespace std.

Kjell