Fix more 'cpo' issues in runtime files.
diff --git a/runtime/ftplugin/cs.vim b/runtime/ftplugin/cs.vim
index 0ff3c9d..7c2cbda 100644
--- a/runtime/ftplugin/cs.vim
+++ b/runtime/ftplugin/cs.vim
@@ -10,6 +10,8 @@
" Don't load another plugin for this buffer
let b:did_ftplugin = 1
+let s:keepcpo= &cpo
+set cpo&vim
" Set 'formatoptions' to break comment lines but not other lines,
" and insert the comment leader when hitting <CR> or using "o".
@@ -22,3 +24,6 @@
let b:browsefilter = "C# Source Files (*.cs)\t*.cs\n" .
\ "All Files (*.*)\t*.*\n"
endif
+
+let &cpo = s:keepcpo
+unlet s:keepcpo