Don't override command completions with init script ones.

Need to be more careful with these now as some command completions may already
be set up before contrib/service is sourced and we want them to survive.

contrib/service

@@ -34,7 +34,8 @@ _service()
 } &&
 complete -F _service service
 [ -d /etc/init.d/ ] && complete -F _service -o default \
-    $(for i in /etc/init.d/*; do printf '%s\n' ${i##*/}; done)
+    $(for i in /etc/init.d/*; do
+    complete -p ${i##*/} &>/dev/null || printf '%s\n' ${i##*/}; done)
 
 # Local variables:
 # mode: shell-script