Ensure that remote operations are not only lazily evaluated.

This checkin adds a Force() operation that will force the evaluation
of any operation, although at the moment that only applies to
Raster operations.
Added operation for getting RasterLayerInfo from name or path.
Added task for displaying ARG raster info.
Fixes to gtloader
Added raster data type in layer information for admin site.
Fixed tiled mtsthelens rasters.
Refactored how cache is given propagated through catalog.
Merge pull request #495 from joshmarcus/topic/lazy

Ensure that remote operations are not only lazily evaluated.
Merge remote-tracking branch 'upstream/master' into cache/fix
Set in RasterLayerInfo whether or not the layer is cached.
Fixed path in metadata for converting tiles.
Fixed metadata for mtsthelens rasters in test data.
Improvements and bugfix to remote execution of operations.

This checkin resolves one bug where operations designed for remote
execution were not being dispatched, adds a "remote()" method to
operations for sending an operation for remote execution (as opposed
to dispatch() which sends an operation's children), and adds some
documentation.
Merge pull request #496 from lossyrob/cache/fix

Fixes to cache propagation
Merge pull request #497 from joshmarcus/topic/remote

Improvements and bugfix to remote execution of operations.