Problem: Various inconsistencies in test files.
Solution: Add modelines where they were missing. Use Check commands instead
of silently skipping over tests. Adjust indents and comments.
(Ken Takata, closes#6695)
Problem: Tests using term_wait() can still be flaky.
Solution: Increase the wait time when rerunning a test. (James McCoy,
closes#5899) Halve the initial times to make tests run faster
when there is no rerun.
Problem: Some balloon tests don't run when they can.
Solution: Split GUI balloon tests off into a separate file. (Ozaki Kiichi,
closes#4538) Change the feature check into a command for
consistency.
Problem: Leaking memory in input part of channel.
Solution: Clear the input part of channel. Free the entry. Move failing
command test to a separate file to avoid bogus leak reports
clouding tests that should not leak.
