Provide one pkg-config file for every gst-plugins-base library.

Provide one pkg-config file for every gst-plugins-base library.

Original commit message from CVS:
* configure.ac:
* pkgconfig/Makefile.am:
* pkgconfig/gstreamer-audio-uninstalled.pc.in:
* pkgconfig/gstreamer-audio.pc.in:
* pkgconfig/gstreamer-cdda-uninstalled.pc.in:
* pkgconfig/gstreamer-cdda.pc.in:
* pkgconfig/gstreamer-fft-uninstalled.pc.in:
* pkgconfig/gstreamer-fft.pc.in:
* pkgconfig/gstreamer-floatcast-uninstalled.pc.in:
* pkgconfig/gstreamer-floatcast.pc.in:
* pkgconfig/gstreamer-interfaces-uninstalled.pc.in:
* pkgconfig/gstreamer-interfaces.pc.in:
* pkgconfig/gstreamer-netbuffer-uninstalled.pc.in:
* pkgconfig/gstreamer-netbuffer.pc.in:
* pkgconfig/gstreamer-pbutils-uninstalled.pc.in:
* pkgconfig/gstreamer-pbutils.pc.in:
* pkgconfig/gstreamer-riff-uninstalled.pc.in:
* pkgconfig/gstreamer-riff.pc.in:
* pkgconfig/gstreamer-rtp-uninstalled.pc.in:
* pkgconfig/gstreamer-rtp.pc.in:
* pkgconfig/gstreamer-rtsp-uninstalled.pc.in:
* pkgconfig/gstreamer-rtsp.pc.in:
* pkgconfig/gstreamer-sdp-uninstalled.pc.in:
* pkgconfig/gstreamer-sdp.pc.in:
* pkgconfig/gstreamer-tag-uninstalled.pc.in:
* pkgconfig/gstreamer-tag.pc.in:
* pkgconfig/gstreamer-video-uninstalled.pc.in:
* pkgconfig/gstreamer-video.pc.in:
Provide one pkg-config file for every gst-plugins-base library.
This makes linking to those libraries much more intuitive and
provides standard pkg-config behaviour for them. Fixes bug #499697.