FIX resample with fill_method and how #2073
fixes #2073

just needs a whatsnew note otherwise looks good
 @hayd status on this? i can take it if you want ... pretty much done. passing on travis
 If you've done it push it! :)
 ok closing in favor of #7341 (basically just your commits but re run)
 Great, thanks!

confused at the travis: IIRC travis passed, then I squished in some release notes, then it failed.
 looks like a random failure ... since you didn't really touch any of the period index stuff you're just calling fillna which shouldn't change any keys ...
