Further hlint fixes

Commit 2cdaf225, “Re-enable standard hlint warnings”, got it almost
right. The only problem is that (confusingly) the default set of hints
is not in HLint.Default, but in HLint.HLint (it includes Default and
some built-ins).

After changing the lint file to correctly include the defaults, we had
another 128 suggestions:

  - Error: Eta reduce (2)
  - Error: Redundant bracket (4)
  - Error: Redundant do (17)
  - Error: Redundant lambda (7)
  - Error: Redundant return (1)
  - Warning: Avoid lambda (2)
  - Warning: Redundant $ (42)
  - Warning: Redundant bracket (35)
  - Warning: Use : (1)
  - Warning: Use String (4)
  - Warning: Use camelCase (10)
  - Warning: Use section (3)

which are fixed by the current patch. Note that the 10 "Use camelCase"
were all due to hlint not “knowing” the idiom of ‘case_’ (it does for
‘prop_’), for which I filled
http://code.google.com/p/ndmitchell/issues/detail?id=558

.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>