configure.ac: Bump requirements to current core and -base CVS (core for new typefind helper API, and -base for the

Original commit message from CVS:
* configure.ac:
Bump requirements to current core and -base CVS
(core for new typefind helper API, and -base for the
WAVFORMATEX support that was added to libgstriff and
is needed by wavparse).
* gst/apetag/Makefile.am:
* gst/apetag/gsttagdemux.c: (gst_tag_demux_chain),
(gst_tag_demux_sink_activate):
Use new typefind helpers for typefinding instead of our
home-grown stuff; also, do typefinding in pull-mode if
upstream supports that.