add check for k exceeding the number of available palettable colors
add check for k exceeding the number of available palettable colors

lanselin/pysal,TaylorOshan/pysal,pysal/pysal,TaylorOshan/pysal,sjsrey/pysal,ljwolf/pysal_core,ljwolf/pysal_core,hasecbinusr/pysal,sjsrey/pysal_core,ljwolf/pysal,lixun910/pysal,sjsrey/pysal_core,hasecbinusr/pysal,sjsrey/pysal_core,ljwolf/pysal,weikang9009/pysal,ljwolf/pysal,ljwolf/pysal_core,hasecbinusr/pysal,TaylorOshan/pysal,lixun910/pysal,pedrovma/pysal,lixun910/pysal