mapbox/mbxmapkit — pull request #92 by incanus (2014-05-01 22:38:16+00:00)
Title: more descriptive background blocks

This is pretty minor, but inside the implementation of `MBXRasterTileOverlay`, `dataBlock` doesn't indicate enough to me what's going on. Something like `workerBlock` emphasizes that it's some background work that's happening.

Additionally, in the first case, just pass `nil` instead of an empty block. This is more standard in Apple's APIs.