Add quotes around $action to handle cases where todo.actions.d path includes embedded spaces.

There were a couple places where $action was used without quotes
that caused a problem if the .todo.actions.d had a parent directory
path that included spaces (e.g. /cygdrive/c/Documents\ and\ Settings/jo-user).
This was in the section that calls the addons with the 'usage' arg.

Signed-off-by: Gina Trapani <ginatrapani@gmail.com>

todo.sh

@@ -211,9 +211,9 @@ EndHelp
         echo ""
         for action in "$TODO_ACTIONS_DIR/*"
         do
-            if [ -x $action ]
+            if [ -x "$action" ]
             then
-                $action usage
+                "$action" usage
             fi
         done
         echo ""