ENH: Update LibLinear sources w/instance weights.

Patches LibLinear sources to liblinear-1.94 with support for instance
weights.
ENH: Expose new LibLinear instance weight feature.
ENH: Generalize test_sample_weights 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.