fix: pass warm_start to BaseSGDRegressor
fix: make Regressor test case extend CommonTest (move two clf specifc tests to clf test case)
DOC be more explicit on mean-shift scalability

Fixes #2613.
Merge pull request #2617 from pprett/sgd-regressor-fix

[MRG] pass warm_start to BaseSGDRegressor
some cleanup, conflict fixes, squashes, re-dos
redo typo fixes
small css tweak
FIX stop forcing deprecation warnings for external packages
FIX use of str.format for Py2.6
speedup for docbuild using joblib
change cache directory
Merge pull request #2620 from jaquesgrobler/master

ENH: speedup for docbuild using joblib
pass impurity to ``impurity_improvement`` - now it is correct so that arbitrary Criteria can be used in best-first search.
typo fix
COSMIT + FIX in _utils.pyx
changes to headings and sections
Merge commit 'fbab2cd' into gbm

Conflicts:
	sklearn/tree/_tree.c
remove face-recognition exercises, skeletons, etc and merge artifacts
further changes to headings and subsections
re-order some Documentation categories in documentation.html
fix broken link for stable version from dev version