Plug-in configuration wizard may use invalid default value for item and file parameters

[Nicklas Nordborg]

The plug-in/job configuration wizard automatically selects the item stored in the current context for item and file parameters if they don't have any values. If the parameters are enumerated and the current context item isn't in the enumerated list it all goes wrong.

First, ther parameter is marked as having a value, but when you select it it is cleared. If you don't select another value you will get an error message complaining about trying to use a value that is not in the list of allowed values.

The solution I think is to not use the current context, when the parameter has an enumeration.

[Nicklas Nordborg]

(In [3567]) Fixes #681