Included patch for persistent undo. Lots of changes and added test.

runtime/optwin.vim

@@ -1032,6 +1032,10 @@ if has("vertsplit")
   call append("$", "cmdwinheight\theight of the command-line window")
   call <SID>OptionG("cwh", &cwh)
 endif
+call append("$", "undofile\tautomatically save and restore undo history")
+call <SID>BinOptionG("udf", &udf)
+call append("$", "undodir\tlist of directories for undo files")
+call <SID>OptionG("udir", &udir)
 
 
 call <SID>Header("executing external commands")