FIX: use clip(0) instead of abs()

This removes spurious tiny negatives from the output of eig.
DOC : fix alpha docstring in dict learning
DOC : really fix alpha docstring in dict learning
Revert "DOC : really fix alpha docstring in dict learning"

This reverts commit 645863e0f26fd0ed568972f1373d61e1bb10261a.

@agramfort: sorry: a better read of the code told me that it was
transform_alpha used by the OMP. So alpha is indeed always a float
FIX unused pos_label parameter in metrics.precision_recall_curve
FIX: ENetCV and LassoCV now accept np.float32 input
Merge pull request #3178 from MechCoder/Iss3174

[MRG+1] ENetCV and LassoCV now accept np.float32 input