fixed bootstrap vote (weird average loss compared to results, prediction errors...)

After investigating weird differences between displayed log loss and effective loss on bs vote, discovered many misclassification errors due to an else missing. I now get better results with Bootstrap vote on my data and tests also. I had to modify tests 27 and 28.

I finally didn't touch the loss function code (0. or 1. loss) which does not make use of the main logloss method (see pull request  #359).