Expose d3's stack offset to allow for percent-based stack using 'expand' - fix #225
Keep same reference on data and values for scatter
Remove setup of `singlePoint` variable that is not used in some of the bar models.

Additionally, this variable was being assigned as a property on the global object (`window` in browsers) instead of being declared locally with a `var` statement.
Merge pull request #257 from JustinTArthur/remove-unused-global-singlePoint-var-assignments

Remove singlePoint variable that is assigned but not used in bar models.
Merge branch 'fix-dereferencing' of https://github.com/Marsup/nvd3 into master-issue240
Merge branch 'rb/expose_stacked_offset' of https://github.com/rustybailey/nvd3
Fixed typo in cumulativeLineChart rescaleY() method.