Menubar: Add shell completion to menubar

Since we can search for commands in menubar and easily execute almost
any program now, we can definitely make use of awful.shell.completion,
which is enabled with this commit.

Signed-off-by: Ignas Anikevicius (gns_ank) <anikevicius@gmail.com>
Signed-off-by: Uli Schlachter <psychon@znc.in>

lib/menubar/init.lua.in

@@ -240,10 +240,12 @@ function show(scr)
     current_item = 1
     current_category = nil
     menulist_update()
-    awful.prompt.run({ prompt = "Run app: " }, instance.prompt.widget, function(s) end,
-               nil, awful.util.getdir("cache") .. "/history_menu", nil, hide,
-               menulist_update,
-               prompt_keypressed_callback)
+    awful.prompt.run({ prompt = "Run: " }, instance.prompt.widget,
+                function(s) end,            -- exe_callback function set to do nothing
+                awful.completion.shell,     -- completion_callback
+                awful.util.getdir("cache") .. "/history_menu",
+                nil, hide, menulist_update, prompt_keypressed_callback
+                )
     instance.wibox.visible = true
 end