TST: Assign and index using .loc
TST: Assign and index using .loc

Fix the tests to assign using the loc indexer instead of assigning
to the resulting view. Fixes some pandas warnings.

urschrei/geopandas,koldunovn/geopandas,ozak/geopandas,geopandas/geopandas,perrygeo/geopandas,IamJeffG/geopandas,jorisvandenbossche/geopandas,micahcochran/geopandas,snario/geopandas,scw/geopandas,jdmcbr/geopandas,kwinkunks/geopandas,fonnesbeck/geopandas,jorisvandenbossche/geopandas,jorisvandenbossche/geopandas,micahcochran/geopandas,maxalbert/geopandas,ozak/geopandas,geopandas/geopandas,jdmcbr/geopandas,geopandas/geopandas