[MRG] update sklearn.svm.bounds to use recent helpers

Here was some code with stale conventions. If it is useful code, perhaps it should be available in `linear_model` (and for alpha), not just in `svm`.
yes, I fear it's the wrong term, but don't know what the correct one is.

Basically this error occurs if the sum of a feature when a class is present minus its sum when the class is absent is 0, for all features (including intercept) and classes.

For example, the following raise the error:
* `l1_min_c([[1], [1]], [1, 0], fit_intercept=False)`
* `l1_min_c([[1], [-1]], [1, 1], fit_intercept=False)`
* `l1_min_c([[1], [-.5], [.5]], [1, 1, -1], fit_intercept=False)`

Which leaves me still unsure how to improve the error message?