Fixed bug where 'id' property was used for duplicate checking rather than settings.tokenValue.

[ashic]

add_token was explicitly checking for 'id' property for duplicate checking. If user passed in a tokenValue via settings, 'id' would be undefined. In this case, adding multiple items through $(..).tokenInput('add', {..}) became impossible.

[janhartigan]

Just confirming here that this is exactly what I did to fix this issue as well.