Change to allow multiple calls to write so indices in stress_period_data is not modified.
Change to allow multiple calls to write so indices in stress_period_data is not modified.

bdestombe/flopy-1,aleaf/flopy,jentjr/flopy,jentjr/flopy,brclark-usgs/flopy,brclark-usgs/flopy,aleaf/flopy,mrustl/flopy