PNG image regression testing

Originally committed as revision 25011 to svn://svn.ffmpeg.org/ffmpeg/trunk

tests/lavf-regression.sh

@@ -148,6 +148,10 @@ if [ -n "$do_ppm" ] ; then
 do_image_formats ppm
 fi
 
+if [ -n "$do_png" ] ; then
+do_image_formats png
+fi
+
 if [ -n "$do_bmp" ] ; then
 do_image_formats bmp
 fi

tests/ref/lavf/png

@@ -0,0 +1,3 @@
+c162094e51dc1a3203de43e496086dfd *./tests/data/images/png/02.png
+./tests/data/images/png/%02d.png CRC=0x6da01946
+248612 ./tests/data/images/png/02.png