ENH/TST: add anonymous reading of s3 for public buckets
closes #7246

need to add to requirements for the ones you want to check (maybe just 2.7), test the non-implemented error in the rest?
 ah right thx ... 
 @jreback ok with this?
 will squash 
 one thing is that i use a symlink to avoid copying tips.csv ... will that work on windows?
 worst case i can just copy tips.csv
 looks ok
no idea about the symlink
