desktop-shell: launch from the compositor

Fork and exec desktop-shell in the compositor. This is a way to create
an authenticated client. Later, the desktop-shell interface will be
reserved for this client only.

For exec to work, the compositor should be started from the
wayland-demos' root directory.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>

clients/desktop-shell.c

@@ -323,6 +323,9 @@ int main(int argc, char *argv[])
 		return -1;
 	}
 
+	/* The fd is our private, do not confuse our children with it. */
+	unsetenv("WAYLAND_SOCKET");
+
 	wl_display_add_global_listener(display_get_display(desktop.display),
 				       global_handler, &desktop);