versionExchange: first stab in the dark
only send local version once
compare versions for compatibility
fixed Compatible and added a small test case
dont need coreos/semver yet
don't use my protobuf path
renamed version pkg to handshake
changed message from SemVer to Handshake1
addressed CR by @jbenet
Merge pull request #180 from cryptix/versionHandshake

Version handshake
first JSON RPC command
convert DAGService to an interface
new client subpackage
target Node unexported in Link, accessed by functions

by hiding the Node pointer in Link, Links may be encoded atomically
ipfsc: new RPC client
String() method on merkledag.Node
GetObject, PutObject
key <-> multihash test in util
Text[Marshal|Unmarshal]er for util.Key
api logging