[WIP] Fix LARS on 32 bit Python that failed on Windows

FIX #3370: better LARS alpha path inequality checks for 32 bit support.

Finally fixed the failure reported by AppVeyor (ignore the upload failure, it's because I did not configure the secret key on my personal appveyor account):

  https://ci.appveyor.com/project/ogrisel/scikit-learn/build/job/3enuragixu8bh5r8

The drop for good strategy is no longer triggered by any test as a result of this fix. I did not repove the code for drop for good though.

Ping @fabianp @GaelVaroquaux