glib-unix: New API to watch some Unix signals

This new API allows watching a few select Unix signals;
looking through the list on my system, I didn't see anything
else that I think it'd reasonable to watch.

We build on the previous patch to make the child watch helper thread
that existed on Unix handle these signals in the threaded case.
In the non-threaded case, they're just global variables.

https://bugzilla.gnome.org/show_bug.cgi?id=644941

glib/gmain-internal.h

@@ -0,0 +1,35 @@
+/* gmain-internal.h - GLib-internal mainloop API
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#if !defined (GLIB_COMPILATION)
+#error "This is a private header"
+#endif
+
+#ifndef __G_MAIN_INTERNAL_H__
+#define __G_MAIN_INTERNAL_H__
+
+#include "gmain.h"
+
+G_BEGIN_DECLS
+
+GSource *_g_main_create_unix_signal_watch (int signum);
+
+G_END_DECLS
+
+#endif /* __G_MAIN_H__ */