Bndtools discards edits without prompting if file changes on filesystem

[kriegfrj]

This is an issue I noticed when working on #1850.

1. Open a bnd.bnd file using the Bndtools editor and make some changes without saving.
2. Edit the bnd.bnd file in another editor (eg, Notepad) and save.
3. Bndtools discards your unsaved edits in the editor without prompting and replaces them with the contents of the updated file on the disk.

More friendly behaviour would be like the default Eclipse editors, which prompt and give the user the opportunity to replace the contents or maybe save your changes elsewhere.