Always do async vs sync correctly in GSocketConnection streams

Previously if a GSocketConnection had a blocking GSocket, it would
sometimes block during asynchonous I/O, and if it had a non-blocking
socket, it would sometimes return G_IO_ERROR_WOULD_BLOCK from
synchronous I/O. This fixes the connection to not depend on the socket
state.

https://bugzilla.gnome.org/show_bug.cgi?id=616458

gio/gsocket.h

@@ -176,6 +176,19 @@ gboolean               g_socket_speaks_ipv4             (GSocket
 GCredentials          *g_socket_get_credentials         (GSocket                 *socket,
                                                          GError                 **error);
 
+gssize                 g_socket_receive_with_blocking   (GSocket                 *socket,
+							 gchar                   *buffer,
+							 gsize                    size,
+							 gboolean                 blocking,
+							 GCancellable            *cancellable,
+							 GError                 **error);
+gssize                 g_socket_send_with_blocking      (GSocket                 *socket,
+							 const gchar             *buffer,
+							 gsize                    size,
+							 gboolean                 blocking,
+							 GCancellable            *cancellable,
+							 GError                 **error);
+
 G_END_DECLS
 
 #endif /* __G_SOCKET_H__ */