Initial plan.
1a. Change AboutDialog to mimic query.Query with respect to _utest and suppression of dialog display and waiting.
1b. Create AboutDialog instance.
2a. Change textview.TextViewer as with AboutDialog. Also change textview functions and AboutDialog methods to pass on _utest.
2b. Simulate keyclicks on buttons and test that root gains appropriate child. Then destroy it.
3. At some point, remove dead code and change now incorrect encoding comment.
Separate issue: add simulated button click tests to test_textview and other popup dialogs. Directly calling commands does not test that buttons invoke the right command.