BUG: axis kw not propogating on pct_change
axis option was not correctly set on fillna in pct_change

Thanks. Can you add a test for this?
 @Tux1 pls add a test for this
 Sorry. It is my first commit.
I made a simple test that shows the issue and my commit fixed it.
Is it okay ?
Thanks
 pls see the contributing docs: http://pandas.pydata.org/pandas-docs/stable/contributing.html

tests / fix should be on a single pr.
 Sorry... Moreover the test was wrong. 
I have made another test which is passed with my patch. That is committed in a single branch, this one.
 pls add a whatsnew note for 0.17.1 (bug fix), use this PR number
 @Tux1 can you rebase / update
 Sorry for several commits. I think that is okay now ? whatsnew edited, commit rebased
 some comments, pls squash when finished
 pls rebase on master / squash, see docs [here](http://pandas.pydata.org/pandas-docs/stable/contributing.html#contributing-your-changes-to-pandas)
 Sorry, my repo is a mess... I will be better next time
 merged via https://github.com/pydata/pandas/commit/334b07641a1dc8c1e7390d01184e114ddde0a7da

thanks!
