Tap needs to take A => Any instead of A => Unit
Added error-appending Validation combinator for "search for success"
mechanics; an alternative to orElse-type behavior that appends errors.
Added tests for Validation#findSuccess
Order for NonEmptyList.
Merge pull request #245 from S11001001/topic/nel-order

Order for NonEmptyList
fix error message in Heap
add a safe tap operator, make clear that the other one is unsafe
Merge pull request #237 into scalaz-seven
Zipper fixes & tests

Ports 6f75ca66 and e4bda754, and reinstates the tests which have been disabled
in 541cf769.

I am not yet entirely sure what happens in ZipperTest: Apparently `===` is not
Scalaz' `Equal` but comes from specs2. This led to some weird test failures in
some cases and compilation errors in other cases (with 2.9 and 2.10 failing
differently). I replaced the problematic occurrences with explicit calls to
`Equal` or `==`.