xorg-libs as a dependency

[Jeremy Huddleston]

xorg-libs is a metaport for all the X11 libs.  All the old XFree86  
dependencies were changed to a port:xorg-libs dependency  
simultaneously about 1-2 months ago.  Nothing should really depend on  
xorg-libs directly.  ports should depend on the specific libs they  
actually need.

To that end, I've gone through the tree and updated most ports that  
were using xorg-libs to instead depend on the specific libs necessary.

These two have xorg-libs dependencies, but I can't see why:
swi-prolog
swi-prolog-devel

The following ports are still unchanged because they failed to compile:
arts
basiliskii
blt
elvis
mit-scheme
oleo
pgplot
pnetlib
tkman
vice
vtk
vtk5
wap11gui
xaos
xli
xrmap

These two are unchanged because I've been working on ppc.  I'll fix  
them when I get back to using an intel box.
kinput2-macim
mono

If you use any of the above ports, I suggest you fix them on your  
own.  They require a nontrivial amount of work to fix, so I gave up or  
didn't bother.

--Jeremy