Option to allow new tag creation when autocomplete up

Normally you can create tags with impunity, but when autocomplete is up, you can only create tags by selecting from the autocomplete list.  Even trying to create a new tag that exists in the list will not work.

This behavior does not make sense to me, but it is the default behavior.  I decided to include an option that would allow you to override this behavior (i.e. still create a new tag when autocomplete is up), defaulting to the old behavior.