Fix warnings.

* gmarkup.c: Fix warnings.

* guniprop.c, gunidecomp.c: Make warnings go away by using
GPOINTER_TO_INT() instead of (int).

* gcompletion.[ch]: Add g_completion_set_compare(),
to allow (for example) using case-insensitive completion.

* gobject/gsignal.c: Fix warnings about possible use of uninitialized
variables, and fix logic that would leave 'node' unset in cases
that it might be used in.

* gobject/glib-genmarshal.c: Fix warning about printf format.

gobject/glib-genmarshal.c

@@ -201,7 +201,7 @@ pad (const gchar *string)
     {
       g_free (buffer);
       buffer = g_strdup_printf ("%s ", string);
-      g_warning ("overfull string (%u bytes) for padspace", strlen (string));
+      g_warning ("overfull string (%lu bytes) for padspace", strlen (string));
 
       return buffer;
     }