Fix some compiler warnings from gcc 4.6

gio/gdbusauthmechanismsha1.c

@@ -652,6 +652,7 @@ keyring_generate_entry (const gchar  *cookie_context,
   lines = NULL;
   new_contents = NULL;
   have_id = FALSE;
+  use_id = 0;
   use_cookie = NULL;
   lock_fd = -1;
 

gio/tests/gdbus-serialization.c

@@ -784,7 +784,6 @@ message_serialize_invalid (void)
       DBusMessage *dbus_message;
       char *blob;
       int blob_len;
-      int i;
       /* these are in pairs with matching length */
       const gchar *valid_utf8_str = "this is valid...";
       const gchar *invalid_utf8_str = "this is invalid\xff";

gio/tests/proxy.c

@@ -278,7 +278,7 @@ use_inet_address (gboolean synchronous)
 {
   GSocketAddressEnumerator *enumerator;
   GSocketAddress *sockaddr;
-  GInetAddress *addr;
+  GInetAddress *addr = NULL;
   guint port = 0;
   gchar **ip_and_port;