mediacontrol API: proper fix for mediacontrol_Instance forward declaration

include/mediacontrol_internal.h

@@ -31,6 +31,13 @@ extern "C" {
 #include <vlc/vlc.h>
 #include "vlc/mediacontrol_structures.h"
 
+typedef struct mediacontrol_Instance {
+    vlc_object_t  *p_vlc;
+    playlist_t    *p_playlist;
+    intf_thread_t *p_intf;
+    int           vlc_object_id;
+} mediacontrol_Instance;
+
 vlc_int64_t mediacontrol_unit_convert( input_thread_t *p_input,
                                        mediacontrol_PositionKey from,
                                        mediacontrol_PositionKey to,

include/vlc/mediacontrol.h

@@ -66,12 +66,9 @@ typedef struct {
 #define mediacontrol_PlaylistException          4
 #define mediacontrol_InternalException          5
 
-typedef struct {
-    vlc_object_t  *p_vlc;
-    playlist_t    *p_playlist;
-    intf_thread_t *p_intf;
-    int           vlc_object_id;
-} mediacontrol_Instance;
+/* mediacontrol_Instance is an opaque structure, defined in
+   mediacontrol_internal.h. API users do not have to mess with it. */
+typedef struct mediacontrol_Instance mediacontrol_Instance;
 
 /* Cf stream_control.h */
 enum mediacontrol_PlayerStatusList