fix issue of pie chart being invisible when total group value is 0
Merge pull request #447
clean up empty pie support

add an empty title property
check if data is empty before running pie
claim that the slice is "others" to override custom accessors
adjust stock example to not show (Inf) percentage in this case

no more accepting NaNs here!
reenable a mysteriously disabled test
update stock fixture
Merge branch 'master' of https://github.com/dc-js/dc.js
Merge branch 'empty-pie'