Dynamo Snapshotting

Tests passing.  This is now using a SNAPSHOT of spray-aws due to the akka-2.2-RC1 dep.  When 2.2 final happens Ill cut a release of spray-aws.

```

> project eventsourced-journal-dynamodb
[info] Set current project to eventsourced-journal-dynamodb (in build file:/Users/scott/github.com/eligosource/eventsourced/)
> it:test
[warn] Credentials file /Users/scott/.sbt/.credentials does not exist
[warn] Credentials file /Users/scott/.sbt/.credentials does not exist
[warn] Credentials file /Users/scott/.sbt/.credentials does not exist
2013-06-26 21:13:03.539 java[44154:7a03] Unable to load realm info from SCDynamicStore
Jun 26, 2013 9:13:06 PM org.apache.hadoop.util.NativeCodeLoader <clinit>
WARNING: Unable to load native-hadoop library for your platform... using builtin-java classes where applicable
[info] DynamoDBJournalSpec:
[info] A journal
[info] - must persist and timestamp input messages
[info] - must persist but not timestamp output messages
[info] - must persist messages with client-defined sequence numbers
[info] - must persist input messages and acknowledgements
[info] - must persist input messages and acknowledgements along with output messages
[info] - must replay iput messages for n processors with a single command
[info] - must tolerate phantom acknowledgements
[info] - recover its counter when started
[info] - reset temporary sender paths for previously persisted output messages
[info] DynamoDBReplaySpec:
[info] A journal
[info]   when used for snapshotted replay
[info]   - must replay to current state from latest snapshot
[info]   - must replay to current state from selected snapshot (sequence number criteria include latest snapshot)
[info]   - must replay to current state from selected snapshot (timestamp criteria include latest snapshot)
[info]   - must replay to current state from selected snapshot (sequence number criteria don't include latest snapshot)
[info]   - must replay to current state from selected snapshot (timestamp criteria don't include latest snapshot)
[info]   - must replay to upper limit from selected snapshot (sequence number criteria don't include latest snapshot)
[info]   - must replay to upper limit from selected snapshot (timestamp criteria don't include latest snapshot)
[info]   - must replay to upper limit from selected snapshot (upper limit tightens selction criteria)
[info]   - must only offer snapshot if snapshot represents current state
[info]   - must only offer snapshot if upper limit excludes messages after snapshot
[info]   when used for non-snapshotted replay
[info]   - must replay all messages
[info]   - must replay all messages if no snapshot could be selected
[info]   - must replay to upper limit
[info]   - must replay to upper limit if no snapshot could be selected
[info]   - must replay from lower limit to upper limit
[info]   - must not replay for lower limit > upper limit
[info] - recognize stored snapshots when started
[info] Passed: : Total 26, Failed 0, Errors 0, Passed 26, Skipped 0
[success] Total time: 36 s, completed Jun 26, 2013 9:13:36 PM

```