mark - work on ct combinations
added close method to RequestDataset.ds

The dataset attached to the RequestDataset was not closing properly. In fact, it may have never been closing properly. A __del__ clause was added to attempt to close the dataset.
improved access to dictionary keys with different capitalizations

Retrieving dictionary keys has been problematic as the case for shapefile attribute names is not handled well throughout the software. Using the _get_ method now attempts to catch the various forms.
mark - start of day
check for spatial aggregation

For the base class OcgFunction, check if the data is aggregated (i.e. spatial dimension of (1,1)) before running the spatial aggregation. A private function was added to do this.
testing for raw and agg

Some new tests were implemented for raw and agg flags on the OcgCalculationEngine. The tests did not fail so internal code was not changes except for a few cosmetic mods.
moved creation of _ds property variable

Exceptions were occurring when a RequestDataset was being deleted
following an error. The _ds private variable was moved up in the
__init__ method to avoid this.
test fixes and debug code

Multiple small fixes for tests. Also added a number of debug messages.
There are some new tests for problematic computations. Fixed an issue
with in calc.base where the shape was not being properly compared for
aggregation.