change default sel_bw kernel type to bisquare to match GWR class
change default sel_bw kernel type to bisquare to match GWR class

ljwolf/pysal,ljwolf/pysal,pedrovma/pysal,lixun910/pysal,ljwolf/pysal,sjsrey/pysal,lixun910/pysal,weikang9009/pysal,lixun910/pysal,lanselin/pysal,pysal/pysal