Don't report error if a relative ID is not found when inserting a menu or menu item.
Also remove a local variable declaration that is override the passed in parameter.
Fix the failure case of inserting before a non-existent reference item. We need to insert it at the end just as we do on the Mac.
Fix typo in comments.
Merge pull request #184 from adobe/rlim/menu-position-api

Don't report error if a relative ID is not found when inserting a menu or a menu item.