Fix cloud sdf example for py3k and make it more portable.
Fix cloud sdf example for py3k and make it more portable.

drufat/vispy,QuLogic/vispy,drufat/vispy,jay3sh/vispy,jay3sh/vispy,srinathv/vispy,julienr/vispy,kkuunnddaannkk/vispy,sh4wn/vispy,ghisvail/vispy,dchilds7/Deysha-Star-Formation,inclement/vispy,inclement/vispy,RebeccaWPerry/vispy,michaelaye/vispy,bollu/vispy,jdreaver/vispy,RebeccaWPerry/vispy,RebeccaWPerry/vispy,sh4wn/vispy,kkuunnddaannkk/vispy,jay3sh/vispy,sbtlaarzc/vispy,ghisvail/vispy,kkuunnddaannkk/vispy,hronoses/vispy,hronoses/vispy,Eric89GXL/vispy,Eric89GXL/vispy,bollu/vispy,dchilds7/Deysha-Star-Formation,julienr/vispy,Eric89GXL/vispy,ghisvail/vispy,jdreaver/vispy,bollu/vispy,hronoses/vispy,QuLogic/vispy,inclement/vispy,sh4wn/vispy,sbtlaarzc/vispy,jdreaver/vispy,QuLogic/vispy,michaelaye/vispy,sbtlaarzc/vispy,srinathv/vispy,drufat/vispy,srinathv/vispy,julienr/vispy,dchilds7/Deysha-Star-Formation,michaelaye/vispy