[Javascript] add a new entry in a drop down menu

[Geoff Corriere]

I do not believe you can have an entry field in a drop down menu. The 
alternative is to instruct the user to select from the existing choices 
in the menu, or add an entry to a text field. Use a little JavaScript 
to make sure the user has not selected from the menu and placed an 
entry in the field, if necessary.

Geoff