1. Removed raised exceptions with polygon.value and grid.corners.
   They now return None to be consistent with other spatial
   objects.
2. Added new functionality for extrapolating corners from 2-d grids.
3. Added new wrapped state code and comparison functions.
Removed two defunct exceptions.
doc changes
Added a get_time_series method to TestBase.
minor
unique season flag returning wrong slice #337

Fixed iter_boolean_groups_from_time_regions to return the correctly
sliced object. The month from a wrapped season is now correctly
appended.
Improved documentation for 'unique' seasonal flag and multi-geometry
subsetting to netCDF.
minor
mark - changed test target
Merge branch 'next' into nose-plugin