Here is really a mistake that I ignore.

I use `MAX_BYTES_ALLOCATION` here to avoid the scenario that a file length is bigger than what an `Int.maxValue` can represent. Mahout implementation just ignore the case, they convert `long` directly into `int`. Though the semantic of the interface is "small file", but we should not limit the input file length for end-user.

I just treat it as bytes array which encapsulated in a `Text`, I will join the slices of a single file together in `smallTextFiles()` interface. Due to the locality of split, I can merge them together without shuffle. But I forget it in this version, I'll fix it now.