ENH: Use new pandas __finalize__ method
ENH: Use new __finalize__ method in GeoDataFrame too
TST: re-enable skipped tests
ENH: Define new _constructor property for GeoPandas objects
     Special fillna method is no longer needed for recent pandas versions.
     Need an extra check in __getitem__ to return a DataFrame if no geometry
TST: fillna needs argument now, and takes method argument
TST: Enable groupby test
BUG: Fix breakage on pandas <= 0.12
TST: Skip groupby test in pandas 0.12; add fillna test asserts
Merge pull request #49 from kjordahl/feature/update_pandas_api

Update GeoPandas objects to new pandas API