ENH: Update LibLinear sources w/instance weights.

Patches LibLinear sources to liblinear-1.94 with support for instance
weights.
ENH: Generalize more tests for LinearSVC.

Scaled sample weights on a linearly-separable dataset cannot cause an
SVM with a linear kernel to misclassify the down-weighted points.

The modified test case changes the linearly-separable dataset to contain
a non-separable outlier. This outlier should be misclassified unless
sample weights are in fact taken into account.
DOC: SVM docs show LinearSVC has sample_weight.
FIX: Behavior of classes_ attr w/new BaseLibLinear

BaseLibLinear and derived classes no longer have a "classes_" attribute
until fit() has been called.