configure.ac: Pull in librfb from my CVS tree, because it is too small and annoying...

configure.ac: Pull in librfb from my CVS tree, because it is too small and annoying to be separate.  Move rfbsrc plug...

Original commit message from CVS:
* configure.ac: Pull in librfb from my CVS tree, because it is
too small and annoying to be separate.  Move rfbsrc plugin
to gst/.
* ext/Makefile.am:
* ext/librfb/Makefile.am:
* ext/librfb/gstrfbsrc.c:
* gst/librfb/Makefile.am:
* gst/librfb/gstrfbsrc.c:
* gst/librfb/rfb.c:
* gst/librfb/rfb.h:
* gst/librfb/rfbbuffer.c:
* gst/librfb/rfbbuffer.h:
* gst/librfb/rfbbytestream.c:
* gst/librfb/rfbbytestream.h:
* gst/librfb/rfbcontext.h:
* gst/librfb/rfbdecoder.c:
* gst/librfb/rfbdecoder.h:
* gst/librfb/rfbutil.h: