Add dpx encoding regression test.

tests/lavf-regression.sh

@@ -183,6 +183,10 @@ if [ -n "$do_pcx" ] ; then
 do_image_formats pcx
 fi
 
+if [ -n "$do_dpx" ] ; then
+do_image_formats dpx
+fi
+
 # audio only
 
 if [ -n "$do_wav" ] ; then

tests/ref/lavf/dpx

@@ -0,0 +1,4 @@
+a80049454fe1f00233be79b87a4f9c07 *./tests/data/images/dpx/02.dpx
+./tests/data/images/dpx/%02d.dpx CRC=0x6da01946
+305792 ./tests/data/images/dpx/02.dpx
+