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This commit adds a Mount abstraction (which is really just
a wrapped context closer). It makes sure to bind the mount
to the fate of the Node (i.e. close it if the node ends).
This fixes #350

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

not internal since io needs it

fix(fuse/ipns) use pb package

fix(fuse) import protos from unixfs/pb package

and other logging switches. I kept the u.PErr and u.POut in cli
commands, as those do need to write raw output directly.

cc @jbenet

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

dependencies are vendored into Godeps/_workspace and commit versions are
recorded in Godeps.json

update datastore to e89f0511
update go.crypto

link errors left:
- protocol buffers output is not lint-friendly