Trigger file selected event when the selected file is the same

[jrochas]

In Add Node Source window, when using the import by file, there is a usability issue that occurs when:

• a file is imported
• then the imported parameters are modified by hand
• then the same file is imported again
  The result is that the parameters that were modified by hand are not overriden by the parameters found in the file. The reason is that since the file that is selected is the same as the previous selection, then the file selected event is not triggered, so the whole parameter filling mechanism is not triggered either. The properties of the FileUpload item (which handles the file import) needs to be investigated to be able to trigger the file selected event even when the same file is selected. This seems not trivial, and GWT version-dependent.