BUG: made behavior of operator equal for CategoricalIndex consistent,…
… improved unit tests

this is a follow-up to https://github.com/pydata/pandas/pull/9947

@jreback 

pls add this issue number (the PR) to the same place as in #9947 (just list it in the whatsnew after)
 sure, just updated the whatsnew 
 couple of doc fixes
 thanks, updated 
 @jreback it's green now, please take a look
 ty!
