Functional tests failing

[rvagg]

Got no time right now to look in to this, would love someone to put up their hand to figure out why 0.18.4 is broken: https://travis-ci.org/rvagg/node-levelup/builds/28288083

[dominictarr]

okay I have reproduced this locally (with a fresh install...)
this is very weird. somewhere it is throwing a buffer!

[dominictarr]

I found it. downgrading to concat-stream@0.1 to fixes this.
the problem is that in concat stream the first argument isn't an error.
there is an issue describing it here: max-mapper/concat-stream#6

Now, I would have probably still used an always null error arg for consistency with node patterns.