ENH: add interval kwarg to get_data_yahoo issue #9071
PR for the issue #9071

needs some tests for this
 The Travis CI builds fail for an import error in an unrelated module. The PR pass all tests locally.

@jreback OK
 you have to add tests to the PR
 Added tests for 'monthly', 'dividend' and invalid intervals in test_get_data_interval.
 @jreback I think the PR is ready for merge, the Travis CI failures "ERROR: Failure: ImportError (cannot import name json)" are unrelated to my change. All tests related to the pandas.io.data module pass on my machine with python2.7 and python3.4.

Is there anything more I can do?
 pls add a release note (enhancements section, referencing the issue).

rebase on master and you should be good. ping on green.
 Hopefully I did the rebase correctly.

I can't make sense of the Travis CI errors, some are unrelated to my changes and at least one appears to be a temporary failure of Yahoo! CSV API. I used the changes extensively a few days ago, so I'm quite confident of the code, but I experienced intermittent failures of the CSV API today.

IMO the PR can be merged as is. Thanks.
 @alexamici well it appears to be failing on the routine you changed. 
 @jreback short story: this is quite embarrassing, but the test function I wrote was total crap and I didn't notice as it was being skipped in my local testing. Now all should be well.

Long story: to my partial excuse I usually use py.test assert or doctests so I had no prior experience with assertEqual and friends, and I made a mess of the test function. Furthermore when running locally my tests were skipped due to lxml missing and I didn't figure it out until today. Last but not least, I was using the 'GOOG' symbol that has been redefined recently and queries for 2013 resulted in a Yahoo! API failure.
 Tests are passing now! @jreback this is OK?
 thanks @alexamici !
 btw, if you would like to review the docs in remote.rst for any updates
(looking for a general review, not necessarily tied to this change).
