Fixed the longstanding xterm problem.

For ages I've had problems with 256-color xterm and vim.  I never
used a proper colorscheme, but just modified the default I was
"magically" given.  This changes all of that to make us now have
a proper color scheme -- the "adam" scheme.

Colors now work independent of console color depth, I think.
There are remaining quirks, but I'll have to add the requirements
as proper color mappings to my color scheme file.

vim/vimrc.globalprefs

@@ -40,6 +40,4 @@ set wildmenu
 
 set mps+=<:>
 
-if &term =~ "rxvt"
-    set t_Co=16
-endif
+set history=8192