DOC allow link embedding to proceed when web sites unavailable
FeatureUnion example using a heterogeneous datasource.

Uses the 20newsgroups dataset. Extracts & processes the subject-line and body
with separate pipelines and combines them with a FeatureUnion.
DOC RidgeCV more explicit documentation of CV parameter, taken from GridSearchCV.
Merge pull request #3571 from jnothman/fix-link-embedding

[MRG] DOC allow link embedding when some sites not available
MAINT CI: collect rackspace DNS info

Sometimes the following installation step fails:

    pip install -r continuous_integration/appveyor/requirements.txt

This steps download prebuilt version of numpy and scipy for windows that
are hosted on a rackspace container. In order to be able to report
the necessary debugging info to the rackspace cloud support team we need
to know the location of the failing hosts.