Favor execute() over :redir to minimize side effects

If this is still unacceptable for users of ancient versions of Vim, we
could further change the else clause to `return 1`.

Resolves: #182

plugin/sensible.vim

@@ -21,9 +21,13 @@ endif
 " overriding options in the user's vimrc, but still override options in the
 " system vimrc.
 function! s:MaySet(option) abort
-  redir => out
-  silent verbose execute 'setglobal' a:option . '?'
-  redir END
+  if exists('*execute')
+    let out = execute('verbose setglobal ' . a:option . '?')
+  else
+    redir => out
+    silent verbose execute 'setglobal' a:option . '?'
+    redir END
+  endif
   return out !~# ' \~[\/]'
 endfunction