Local operations updated to use helper operations in place of traits. 

As part of the effort to make local operations work transparently on tiled rasters, the local operations are redefined in this pull request to use new helper operations in place of directly invoking methods on actual raster instances.  This keeps the abstraction at a single level and gives us a single point in which we can handle operations on distributed rasters.

As this involved updating every local operations, I ended up fixing some naming issues and bugs as well.