DOC allow link embedding to proceed when web sites unavailable
FIX raise error when number of features changes in partial fit, Add common test for inconsisten number of features for partial fit.
Fixed issue 3815. Discrete AdaBoostClassifier now fails early if the base classifier if worse than random.
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.
MAINT try to avoid HTTP timeouts to rackspace
Update about page
Remove unused distance calculation from clustering example.
DOC link to NLTK website

[ci skip]
FIX #2986: ZeroDivisionError in LinearRegression on sparse data
DOC FIX: typo and minor update
Merge pull request #3854 from justmarkham/doc-changes

DOC FIX: typo and minor update
Merge pull request #3833 from amueller/sgd_partial_fit_variable_length

[MRG] TST raise error when number of features changes in partial fit
Merge pull request #3853 from ogrisel/backport-lsqr-fix

[MRG] Fix ZeroDivisionError in LinearRegression on sparse data
TST stronger non-regression test for #3815

Also fixed the testing imports.
Merge branch 'pr/3837'

Fixes gh-3815.
FIX make assert_raises_regex backport for 2.6 consistent with 2.7+

Use regex.search instead of regex.match.

Furthermore, silence the deprecation warning from Python 3.4 as
assert_raises_regexp is now deprecated in favor of the shorter name:
assert_raises_regex.
Merge pull request #3861 from ogrisel/fix-python-2.6-test

[MRG] FIX make assert_raises_regex backport for 2.6 consistent with 2.7+