ext/libpng/gstpngenc.*: Added newmedia support to pngenc so now gst-launch-0.8 videotestsrc ! ffmpegcolorspace ! pnge...

Original commit message from CVS:
2004-07-30  Zaheer Abbas Merali  <zaheerabbas at merali dot org>

* ext/libpng/gstpngenc.c: (gst_pngenc_class_init),
(gst_pngenc_init), (gst_pngenc_chain), (gst_pngenc_get_property),
(gst_pngenc_set_property):
* ext/libpng/gstpngenc.h:
Added newmedia support to pngenc so now gst-launch-0.8 videotestsrc ! ffmpegcolorspace ! pngenc snapshot=false newmedia=true ! multifilesink location=blah%d.png works as expected