Added gst_bytestream_get_timestamp() call to get timestamp of data at the front of the stream.  If no data in stream,...

Original commit message from CVS:
Added gst_bytestream_get_timestamp() call to get timestamp of data at
the front of the stream.  If no data in stream, loads 1 byte to get a
new buffer and uses its timestamp.

Does nothing to handle readers that try to read data lengths that span
buffers with multiple timestamps.

_get_timestamp() now used when creating new buffers.