add FF_API_FIRST_FORMAT define to drop deprecated first_?format from public api

Originally committed as revision 25489 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/avformat.h

@@ -78,6 +78,9 @@
 #ifndef FF_API_PARAMETERS_CODEC_ID
 #define FF_API_PARAMETERS_CODEC_ID     (LIBAVFORMAT_VERSION_MAJOR < 53)
 #endif
+#ifndef FF_API_FIRST_FORMAT
+#define FF_API_FIRST_FORMAT            (LIBAVFORMAT_VERSION_MAJOR < 53)
+#endif
 
 /**
  * I return the LIBAVFORMAT_VERSION_INT constant.  You got
@@ -895,7 +898,7 @@ typedef struct AVPacketList {
     struct AVPacketList *next;
 } AVPacketList;
 
-#if LIBAVFORMAT_VERSION_INT < (53<<16)
+#if FF_API_FIRST_FORMAT
 attribute_deprecated extern AVInputFormat *first_iformat;
 attribute_deprecated extern AVOutputFormat *first_oformat;
 #endif

libavformat/utils.c

@@ -110,8 +110,14 @@ static void av_frac_add(AVFrac *f, int64_t incr)
 }
 
 /** head of registered input format linked list */
+#if !FF_API_FIRST_FORMAT
+static
+#endif
 AVInputFormat *first_iformat = NULL;
 /** head of registered output format linked list */
+#if !FF_API_FIRST_FORMAT
+static
+#endif
 AVOutputFormat *first_oformat = NULL;
 
 AVInputFormat  *av_iformat_next(AVInputFormat  *f)