(PR#10203) Greedy CM algorithm

<URL: http://rt.freeciv.org/Ticket/Display.html?id=10203 >

> > Also, can you send a patch that does not include the old cm code, and 
> > that makes the necessary changes to the rest of the code 
> > (auto_arrange_workers)?

Here's the most minimal patch: it changes only cm.c and leaves the API untouched.
I went through and cleaned up the comments and a couple violations of the
coding standards.

One place I'm knowingly violating standards is that I have the 75-* comments 
demarking sets of related functions rather than demarking every function; then
I use a couple lines of normal C comments to document the function.  I find this
clarifies the overall structure of the code, but I don't feel strongly about this so
if y'all don't like it, I can easily change it.