Add more library to the GStreamer library search.

Note: the gstreamer 0.10 package comes with 5 libraries and we only
check for one. In addition, we check for a library that comes from the
gstreamer-plugins-base 0.10 package.

I suggest this be cleaned up. The extra library can go into
FindGStreamerPlugins.cmake file.

svn path=/trunk/KDE/kdelibs/; revision=771265