You *must* have the plib library installed on your system to build
the FGFS simulator!"

You can get the original library from:

    http://www.woodsoup.org/~sbaker/plib/

This library is also mirrored (identical) at:

    ftp://ftp.flightgear.org/pub/fgfs/Source/plib-1.0.2.tar.gz

Build notes:

When you run "./configure" to configure the package, plib's defaults
to installing the headers in /usr/local/plib/include and the libraries
in /usr/local/plib/lib.

If you would prefer to install these in /usr/local/include/plib/ and
/usr/local/lib, then run configure with the following options:

    ./configure --prefix=/usr/local --includedir=/usr/local/include/plib

Installing like this makes it much easier for the fgfs configure script
to locate the plib includes and libs.