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if the underlying reader is buffered with a smaller buffer
it would force the chunk sizes to come out smaller than
intended.

cc @whyrusleeping @mappum

- distinguish log.Error and log.Errorf functions
- Initialize structs with field names
- A bit of unreachable code (defers)

cc @jbenet

working on dag modification structures, factored out the data format into an importer subpackage and added more ipns tests