BUG/WIP: fix pivot with nan indexes
closes #7466
- [ ] vbench
- [ ] make sure there isn't a better way to do this

seems ok...(though didn't look real close :)
 haven't found the time to do the vbench ... not reeally a whole of time when i don't have abunch of things running (except when i'm sleeping :)
 I moved these to 0.15.0, but if you are ok then can throw in 0.14.1
 ok just not too comfortable with this fix yet, we can wait until 0.15.0
 @cpcloud status? (if not move to 15.1)
 I think #9292 (and #9061) fixed all of these
