driver: Followup to last: make the value more unique.

Part of issue #305.

zsh-syntax-highlighting.zsh

@@ -249,6 +249,7 @@ _zsh_highlight_call_widget()
 _zsh_highlight_bind_widgets()
 {
   setopt localoptions noksharrays
+  typeset -F SECONDS
   local prefix=orig-s$SECONDS-r$RANDOM # unique each time, in case we're sourced more than once
 
   # Load ZSH module zsh/zleparameter, needed to override user defined widgets.