No need to process each L.ByteString chunk, instead ask it to split.
Doesn't seem to have really sped things up much, but it also made the code
simpler.
Note that this does (and already did) buffer in memory. It seems that only
the directory special remote could take advantage of streaming chunks to
files w/o buffering, so probably won't add an interface to allow for that.
c3af4897c0