Tag yahoo data tests as @network only
this ok to merge? 
 https://www.travis-ci.org/pydata/pandas/jobs/7992099

@gliptak @hayd can you look at this.....

need to handle better a failure to get data....not sure of the current standard, raise? 
 @jreback Could you be a bit more specific? I didn't see the actual error in the logs you are pointing to.

I'm also trying to understand why #3817 fails (as it was running without errors locally ...)
 it's an intermittent failure I think because on one test the connection failed
click on the Travis link above
look at the failed build
scroll to the bottom you will see where the test failed
prob just need to put in a better way to handle the None coming back 
 What is a good way to deal with it without it just being skipped? (or is just skipping it if it's None ok?)
 if in general their is a network error what do u do raise some urlopen error?
just catch that and skip in that case

in fact should probably have your new requests pr raise a common NetworkError or something
 @jreback These are new tests for existing (and functionally unmodified) code, which did not have tests before.

OK, I see it now. I will change the tests to check for None.

```
ERROR: test_get_quote (pandas.io.tests.test_yahoo.TestYahoo)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/virtualenv/python3.2_with_system_site_packages/lib/python3.2/site-packages/pandas-0.11.1.dev_e958833-py3.2-linux-x86_64.egg/pandas/io/tests/test_yahoo.py", line 46, in test_get_quote
    assert_series_equal(df.ix[0], df.ix[2])
AttributeError: AttributeError: 'NoneType' object has no attribute 'ix'
-------------------- >> begin captured stdout << ---------------------
Failed to download:
<urlopen error [Errno 111] Connection refused>
```
