Fix handling of SIGCHLD

The commit that removed metacity-dialog added a global SIGCHLD handler
that caused problems by (a) calling waitpid(-1) and thus breaking
g_child_watch for everyone else, and (b) doing too much from a signal
handler and sometimes causing deadlocks (bug 596200).

This removes the global handler and has each zenity user create its
own child watch to watch for exit. (It also fixes the window class of
the zenity dialogs, so that meta_window_present_delete_dialog() will
work again.)

src/core/util.c

@@ -40,8 +40,6 @@
 #include <X11/Xlib.h>   /* must explicitly be included for Solaris; #326746 */
 #include <X11/Xutil.h>  /* Just for the definition of the various gravities */
 
-MetaNexus *sigchld_nexus;
-
 #ifdef HAVE_BACKTRACE
 #include <execinfo.h>
 void
@@ -560,7 +558,7 @@ meta_show_dialog (const char *type,
   int i=0;
   GPid child_pid;
   const char **argvl = g_malloc(sizeof (char*) *
-                                (15 +
+                                (17 +
                                  g_slist_length (columns)*2 +
                                  g_slist_length (entries)));
 
@@ -568,6 +566,8 @@ meta_show_dialog (const char *type,
   argvl[i++] = type;
   argvl[i++] = "--screen";
   argvl[i++] = screen_number_text;
+  argvl[i++] = "--class";
+  argvl[i++] = "mutter-dialog";
   argvl[i++] = "--title";
   /* Translators: This is the title used on dialog boxes */
   argvl[i++] = _("Mutter");
@@ -641,31 +641,6 @@ meta_show_dialog (const char *type,
   return child_pid;
 }
 
-GType
-meta_nexus_get_type (void)
-{
-  static GType nexus_type = 0;
-
-  if (!nexus_type)
-    {
-      static const GTypeInfo nexus_info =
-      {
-        sizeof (MetaNexusClass),
-	NULL, NULL, NULL, NULL, NULL,
-	sizeof (MetaNexus),
-	0,
-	NULL, NULL
-      };
-
-      nexus_type = g_type_register_static (G_TYPE_OBJECT,
-					   "MetaNexus",
-					   &nexus_info,
-					   0);
-    }
-
-  return nexus_type;
-}
-
 /***************************************************************************
  * Later functions: like idles but integrated with the Clutter repaint loop
  ***************************************************************************/