Bulletproof upgrade to DT4 (and rollback to DT3)

[Charles56]

@chreliot

In my experience, and I suspect generally, it now works to:

1. Quit DT3.
2. Download, install, and launch DT4.
3. Delete DT3.

In my case, and no doubt for others, I had to delete the DT3 app before I could install DT4.

Discussed at some length here.