Do this over 0.4.0. remember we dont want to rebase all the things

At this point anything that touches logging will cause merge conflict regardless if it is put into master or dev0.4.0.

In fact, most of the conflicts with 0.4.0 are logging.
Tried a rebase https://github.com/rht/go-ipfs/tree/dev0.4.0-rebase with the changelog:

1. 7eaebfa (because shellquote was added)
2. 9974f56
3. 2f3f582 (There was a WriteLen refactor)
4. 1cb0ee2 (because go-log was added)
5. 4f2a226 (because go-log was added)
6. 9d2bd05 (because go-log was added, leveldbDS no longer a field of FSRepo, ds.Close method, redo 35a5ca0)
7. 681c5d9 (because go-log was added)
8. 6e49de0 (comment rename ThreadSafeDatastore -> Datastore, and uses the go-datastore in 0.3.8-dev branch because it is most likely more up to date, I can't find go-datastore@47af23f2ad09237ccc09c586c118048e2b39b358)
9. 45d3d5b (go-datastore in 0.3.8-dev is newer)
10. 72c0282 (redo 192ee64)
11. de41a9f (module conflict unixfs)
12. d69891f (unixfs -> uio)

The trickiest part is in the datastore conflicts, but can't be sure unless @whyrusleeping is doing it (RFCR).

if you do this on master, it will conflict with every single commit on 0.4.0 that touches any of the same code you touched here.

Will redo the PR after 0.4.0 is merged. Also it's not performance critical, and doesn't fix any bugs.

sounds good

was this always just a three line change? I'm totally fine merging just this.

Because the commits with conflicts were removed.