add support for AVI files with On2 header

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@10591 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/avidec.c

@@ -61,6 +61,7 @@ static const char avi_headers[][8] = {
     { 'R', 'I', 'F', 'F',    'A', 'V', 'I', ' ' },
     { 'R', 'I', 'F', 'F',    'A', 'V', 'I', 'X' },
     { 'R', 'I', 'F', 'F',    'A', 'V', 'I', 0x19},
+    { 'O', 'N', '2', ' ',    'O', 'N', '2', 'f' },
     { 0 }
 };