Add Accumulation to hydrology operations
fixed Accumulation.scala in hydrology

changed from using two stacks to using tuples.
Solved the DataSource Manifest\covariance puzzle.

- Cleaned up the OpX package functions that were unused.
- Got rid of that LoadRasterUrl warning.
- A lot more things are covariant now
Merge pull request #591 from lossyrob/localOpMethods

Solved the DataSource Manifest\covariance puzzle.
Improvements towards new datasource remoting.

This commit includes upgrading to akka 2.2.1, updates to the dev subproject
to run under akka 2.2.1, as well as new changes to the Server actor infrastructure,
a new RemoteOperation wrapper operation, and a distribute() method on DataSourceLike.
Added RasterSource methods for +,-,*,/
Merge pull request #590 from wzjchen/hydrology

Hydrology - Flow Direction
Update FlowDirectionSpec.scala

Removed blank spaces.
Fix command line argument for dev project port.
Fixing subproject builds
Mark Cache as Serializable.
Upgrade Server cluster code and dev project for akka 2.2.1.
Fix to zonal.summary.Mean. Closes #587
Merge pull request #595 from lossyrob/fix/zonalmean

Fix to zonal.summary.Mean. Closes #587
Removed Option[] from Raster.asArray,.mutable,.force
Merge pull request #593 from joshmarcus/topic/ds_remoting

Improvements towards new datasource remoting.
History now includes node identification information.

The History object now includes a string which identifies the node that
an operation was executed on, if a node has a default external address.

The toString() method will include the system id string, but has an optional
boolean argument to exclude it.
Merged in upstream, fixed tests.
Forward RemoteOperations at the dispatcher level.
Update dev/cluster client to use data sources.