Backfill Task.handle unit tests.
Add handleWith to Task.
fix zip

should not evaluate second parameter if first parameter is empty
override apply2, tuple2
add ZipTest
Merge branch 'scalaz-seven' into topic/handle-with

Conflicts:
	tests/src/test/scala/scalaz/concurrent/TaskTest.scala
Merge pull request #625 from xuwei-k/zipLazy

fix zip. should not evaluate second parameter if first parameter is empty
Merge pull request #592 from rossabaker/topic/handle-with

Add handleWith to Task.