TEST: metrics sample_weight test: almost_equal

The test was too strict and failing on certain boxes
FIX bug where distances were of illegal shape
FIX expit bug with out != None
TST hashing vectorizer behavior with np.nan input
DOC: expand documentation for logistic regression
TYPO remove mutli (did you mean Muttley?)
Turn useless line of code into descriptive comment
FIX potential overflow in _tree.safe_realloc

The multiplication with the sizeof the base type may overflow, esp.
on 32-bit machines with very large datasets, causing the function to
allocate less memory than was intended, without not raising an exception.
FIX RFE + test

Quick fix on grid_scores, updating final value with len(cv)
self.grid_scores_ = scores / len(cv)
MISC: avoid overridding figure in benchs
[DOC] minor fixes
Catch ConvergenceWarning in RandomizedL1
MAINT get rid of NumPy DeprecationWarnings

'using a non-integer number instead of an integer will result in an error in the future'
Added a parameter check on n_estimators in BaseEnsemble to raise error if it is not strictly positive.
DOC mention doc-building dependency on Pillow
FIX Py3k support for out-of-core example