added popup for handling SIGSEGV or SIGFPE

the popup is placed on each of the virtual screens
the user can decide to restart or quit i3
in case of an exit a core-dump is generated

include/sighandler.h

@@ -0,0 +1,21 @@
+/*
+ * vim:ts=8:expandtab
+ *
+ * i3 - an improved dynamic tiling window manager
+ *
+ * © 2009 Michael Stapelberg and contributors
+ * © 2009 Jan-Erik Rediger
+ *
+ * See file LICENSE for license information.
+ *
+ */
+#ifndef _SIGHANDLER_H
+#define _SIGHANDLER_H
+
+/*
+ * Setup signal handlers to safely handle SIGSEGV and SIGFPE
+ *
+ */
+void setup_signal_handler();
+
+#endif