avfilter: Add repeatfields filter (Port of mp=softpulldown)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/allfilters.c

@@ -184,6 +184,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER(PULLUP,         pullup,         vf);
     REGISTER_FILTER(QP,             qp,             vf);
     REGISTER_FILTER(REMOVELOGO,     removelogo,     vf);
+    REGISTER_FILTER(REPEATFIELDS,   repeatfields,   vf);
     REGISTER_FILTER(ROTATE,         rotate,         vf);
     REGISTER_FILTER(SAB,            sab,            vf);
     REGISTER_FILTER(SCALE,          scale,          vf);