Properly die when the X server dies

When the X connection breaks for whatever reason, awesome wouldn't properly
exit, but go into a busy loop instead. Fix this by dying when our connection to
the X server dies.

Signed-off-by: Uli Schlachter <psychon@znc.in>

awesome.c

@@ -249,7 +249,10 @@ a_xcb_check_cb(EV_P_ ev_check *w, int revents)
 static void
 a_xcb_io_cb(EV_P_ ev_io *w, int revents)
 {
-    /* empty */
+    /* a_xcb_check_cb() already handled all events */
+
+    if(xcb_connection_has_error(globalconf.connection))
+        fatal("X server connection broke");
 }
 
 static void