ext/flac/gstflacenc.c: Set an estimate for the total number of samples that will be encoded if possible to help decod...

Original commit message from CVS:
* ext/flac/gstflacenc.c: (gst_flac_enc_query_peer_total_samples),
(gst_flac_enc_sink_setcaps), (gst_flac_enc_write_callback):
Set an estimate for the total number of samples that will be encoded
if possible to help decoders if the streaminfo can't be rewritten
later (like when muxing into Ogg containers).
Add a warning if we get header packets after data packets as those
will get lost when muxing into Ogg, i.e. rewriting the headers doesn't
work.