gst/auparse/gstauparse.*: Rewrite auparse to suck a little bit less: make source pad dynamic, so decodebin/playbin wo...

Original commit message from CVS:
* gst/auparse/gstauparse.c: (gst_au_parse_base_init),
(gst_au_parse_class_init), (gst_au_parse_init),
(gst_au_parse_reset), (gst_au_parse_add_srcpad),
(gst_au_parse_remove_srcpad), (gst_au_parse_parse_header),
(gst_au_parse_chain), (gst_au_parse_src_convert),
(gst_au_parse_src_query), (gst_au_parse_handle_seek),
(gst_au_parse_sink_event), (gst_au_parse_src_event),
(gst_au_parse_change_state):
* gst/auparse/gstauparse.h:
Rewrite auparse to suck a little bit less: make source pad
dynamic, so decodebin/playbin work with non-raw formats
like alaw/mulaw; add query function for duration/position
queries; check whether we have enough data before attempting
to parse the header (instead of crashing when that is not the
case); work around audioconvert sucking by swapping endianness
to the native endianness ourselves for float formats; send
initial newsegment event. Fixes #161712.