MISC: remove reference to deprecated Ward
MISC: replace 'assert' with actual ValueError

Addresses comment by @NelleV
MISC: increase test coverage and cosmetics
MISC+DOC: documentation for FeatureAgglomeration

and many cosmetic comments points out in review.
COSMIT: many cosmetic comments

Fixes remarks by @ogrisel, @agramfort, @larsman, @jnothman
FIX: fix failing doctest
DOC: link FeatureAgglomeration better to dim red
MISC: documentation and cosmits

Address comments by @jnothman
BUG: work aroundd Cython bug to build with clang

This commit should work around a Cython bug that makes the previous
iteration code in fast_dict.pyx impossible to compile under clang. See
https://mail.python.org/pipermail/cython-devel/2013-April/003566.html
Merge branch 'master' into hc_linkage

Conflicts:
	doc/whats_new.rst
changing formatting of documentation
Merge remote-tracking branch 'upstream/master' into rbmbranch
STY Simplify and avoided numpy warnings in imputation
MAINT remove useless import
ENH more optimizations for RBM

Shaved off another ~12% on the digits example; the biggest part of the
savings is in _sample_visibles.
Fix a minor typo: 'They requires' should be 'They require'.
Merge pull request #2920 from yoni/master

Fix a minor typo: 'They requires' should be 'They require'.
[Cross Validation] Use itertools.izip consistently across Python 2/3
when computing folds in StratifiedKFold.

This isn't an especially hot code path, but it seemed to be preferable
for consistency.
Merge pull request #2925 from ajtulloch/izip-cross-validation

ENH Use izip consistently in StratifiedKFold
FIX #2924: make lobpcg test pass with reference and ATLAS impl of LAPACK