Ensure av_tree_insert() is defined before using it.

Patch by Carl Eugen Hoyos   cehoyos _at_ ag.or.at

Originally committed as revision 10083 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/nut.c

@@ -20,6 +20,7 @@
  */
 
 #include "nut.h"
+#include "tree.h"
 
 unsigned long av_crc04C11DB7_update(unsigned long checksum, const uint8_t *buf, unsigned int len){
     return av_crc(av_crc04C11DB7, checksum, buf, len);