Get original P.E.Op.S code to compile on modern linux

[JMarlin]

My original plan was to simply compile all of the core P.E.Op.S sources into object files and then link them to a main.c that just calls the GPUStartup or some such thing as my first step towards getting things going, but it looks like this thing was written to run on OG GTK, which nothing really supports anymore, so I'm going to need to either update those parts to work with modern GTK2 or GTK3 or -- and this would probably be a better idea -- just discard the components that use GTK entirely (because we won't be needing the config and about dialogs &c.)