lib/sign: allow to build with glib version less than 2.44

Ubuntu 14.04 uses glib-2.40 which have no some shiny macroses
for interface declaration.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>

src/libostree/ostree-sign.h

@@ -33,16 +33,26 @@
 #include "ostree-remote.h"
 #include "ostree-types.h"
 
-/* Special remote */
-#define OSTREE_SIGN_ALL_REMOTES "__OSTREE_ALL_REMOTES__"
-
-
 G_BEGIN_DECLS
 
 #define OSTREE_TYPE_SIGN (ostree_sign_get_type ())
 
+_OSTREE_PUBLIC
+GType ostree_sign_get_type (void);
+
+G_GNUC_BEGIN_IGNORE_DEPRECATIONS
+typedef struct _OstreeSign OstreeSign;
+typedef struct _OstreeSignInterface OstreeSignInterface;
+
+static inline OstreeSign *OSTREE_SIGN (gpointer ptr) { return G_TYPE_CHECK_INSTANCE_CAST (ptr, ostree_sign_get_type (), OstreeSign); }
+static inline gboolean OSTREE_IS_SIGN (gpointer ptr) { return G_TYPE_CHECK_INSTANCE_TYPE (ptr, ostree_sign_get_type ()); }
+static inline OstreeSignInterface *OSTREE_SIGN_GET_IFACE (gpointer ptr) { return G_TYPE_INSTANCE_GET_INTERFACE (ptr, ostree_sign_get_type (), OstreeSignInterface); }
+G_GNUC_END_IGNORE_DEPRECATIONS
+
+/* Have to use glib-2.44 for this
 _OSTREE_PUBLIC
 G_DECLARE_INTERFACE (OstreeSign, ostree_sign, OSTREE, SIGN, GObject)
+*/
 
 struct _OstreeSignInterface
 {