Add and fix tests from upstream vim

ftplugin/xf86conf.vim

@@ -0,0 +1,23 @@
+if !exists('g:polyglot_disabled') || index(g:polyglot_disabled, 'xf86conf') == -1
+
+" Vim filetype plugin file
+" Language:             XFree86 Configuration File
+" Previous Maintainer:  Nikolai Weibull <now@bitwi.se>
+" Latest Revision:      2008-07-09
+
+if exists("b:did_ftplugin")
+  finish
+endif
+let b:did_ftplugin = 1
+
+let s:cpo_save = &cpo
+set cpo&vim
+
+let b:undo_ftplugin = "setl com< cms< fo<"
+
+setlocal comments=:# commentstring=#\ %s formatoptions-=t formatoptions+=croql
+
+let &cpo = s:cpo_save
+unlet s:cpo_save
+
+endif