added GIF image format (both read and write)

Originally committed as revision 1541 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/allformats.c

@@ -77,6 +77,7 @@ void av_register_all(void)
     av_register_image_format(&yuv_image_format);
     av_register_image_format(&png_image_format);
     av_register_image_format(&jpeg_image_format);
+    av_register_image_format(&gif_image_format);
 
     /* file protocols */
     register_protocol(&file_protocol);

libavformat/avformat.h

@@ -237,6 +237,7 @@ extern AVImageFormat pgmyuv_image_format;
 extern AVImageFormat yuv_image_format;
 extern AVImageFormat png_image_format;
 extern AVImageFormat jpeg_image_format;
+extern AVImageFormat gif_image_format;
 
 /* XXX: use automatic init with either ELF sections or C file parser */
 /* modules */