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: When there is a backslash in an option ":set -=" doesn't work.
Solution: Handle a backslash better. (Jacob Niehus) Add a new test, merge
in old test.
