fix for #71 by replacing call to chunkifier with direct use of thrift API

[robinkraft]

Implements this comment from issue #71, removing call to chunkifier in favor of using the thrift API directly and avoiding nullable !date field issue.

[danhammer]

+1. short and important. nice. #shipit

[eightysteele]

Nice dude. Only curiosity is why predicate/chunkify was originally a predicate macro. If that's not a problem, #shipit.

[robinkraft]

chunkify has been around for ages, so it might have been needed as a predicate macro while using an earlier version of Cascalog. It's still used elsewhere, and it seems like this issue only comes up when !date is actually nil.

Merging.