Fix a few issues found by newer hlint

Testing with a newer hlint found a few minor issues; but all are real,
valid recommendations:

- don't use "if cond then f x else f y", but "f (if cond then x else y)"
- "if a then b else True" is equivalent to the simpler "not a || b"
- and as usual, one more ignore to our "testing basic properties"
  module

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>