[Simh] Repaired readline hack and Makefile

[Philipp Hachtmann]

Hello,

>>> The dlopen thing is a bit Linux depending :-(
> 
> Nope.  dlopen() is POSIX, and everyone has it these days.
> I recently went through a study of its availability before
> deciding to use it in another project, and now have it
> working nicely in 25+ flavors of Unix.
That's good news!

So, I will re-announce: "The dlopen() thing is quite cool and works on 
most common UNIX or similar platforms, including Linux!"  :-)

Best wishes,
Philipp :-)