Use ff_url_join for assembling URLs, instead of snprintf

This ensures proper escaping of numerical IPv6 addresses.

The RTSP (de)muxer needs its own network initialization, since it isn't
a protocol and url_open hasn't been called yet.

Originally committed as revision 22226 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/rtspenc.c

@@ -116,6 +116,7 @@ static int rtsp_write_close(AVFormatContext *s)
 
     ff_rtsp_close_streams(s);
     url_close(rt->rtsp_hd);
+    ff_network_close();
     return 0;
 }