To csv infs
This branch makes inf/-inf different from nan/None (GH #1919), and also fixes a few bugs with INF and NaN values (GH #2026, #2041).

I'll take a crack at merging this soon. Will have to do so tenderly because of all the merge commits =/ 
 my apologies if I've made this overly complicated. let me know if i can clarify things and what to do differently in the future.
 Generally merging master into a feature branch is discouraged because it makes merging back or cherry-picking messy. Rebasing, if anything at all, tends to be preferable
