clarify pie chart tests
clarify pie chart tests

default should sort by descending value
but you can go back to alphabetical order if u really want]
for #1295

aaronhoffman/dc.js,dc-js/dc.js,aaronhoffman/dc.js,aaronhoffman/dc.js,dc-js/dc.js,dc-js/dc.js,aaronhoffman/dc.js,dc-js/dc.js,aaronhoffman/dc.js,mtraynham/dc.js,mtraynham/dc.js,mtraynham/dc.js,mtraynham/dc.js,dc-js/dc.js,mtraynham/dc.js