Add Accumulation to hydrology operations
fixed Accumulation.scala in hydrology

changed from using two stacks to using tuples.
Initial commit to new fork.
FlowDirection now extends Op1; some formatting changes
Fixed some spelling.
Added some documentation.
Clarified the maps in the getNeighbors function
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.
Made some comments parseable for ScalaDocs; removed unnecessary blank lines/white space.
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