* Replaced code that checks validity of Extra active text with a call to TSnippetValidator.ValidateExtra.
* Moved assertions that ensure that all combo boxes have default items selected.
* Simplified TUserDBEditDlg.UpdateReference: now determine valid dependency snippet kinds with a call to TSnippetValidator.ValidDependsKinds rather than hard wiring the details.
* Modified TUserDBEditDlg.ValidateData to use renamed TSnippetValidator.ValidateDependsList method.
